See attached pdf (link below); some algebra skills are required.
A few tips I think are good for first timers. This is not really a primer about how to DIY, and it will certainly not tell you everything you need to know. In fact, most of this is stuff you don't need to know; it is just a list of bullet points that I think might be helpful, perhaps allowing you to enjoy the DIY learning curve, rather than suffering through it.
Start slow. Do the reading (see links below), and then post any questions you develop. I am not going to reiterate the safety precautions here, but it is more than worth your time to know those things. And if you are not a chemist, the blogs linked below will explain some important things in terms that normal humans can understand. Additionally, there are a lot of great vendors from whom you can buy supplies that are discussed in the DIY forum, and there are some lousy ones out there too (you probably won't read about them on ECF, but they exist); time spent reading general threads on the DIY forum about suppliers is well worth it.
Start slow. When you make your first purchase, don't pile up on labware and flavors. You can get started with a couple of disposable syringes, some empty bottles from pre-made juice, and some VG and/or PG. Nicotine base, if you will use it, and a few flavorings will round it out. Clear packing tape over the markings of disposable syringes will keep them usable for a long time.
Start slow. Make your first mix a small batch of unflavored, and vape some of it. You may like it (I do), but even if not, that allows you to check the quality and flavor of those ingredients. If you can, vape a couple of drops of your PG and/or VG by themselves. Each has a flavor of its own, and some brands/sources are better than others. If one of them is nasty, it's much better to know that now than after mixing up a bunch of juices.
Start slow. Do single flavor mixes of each flavoring before combining them. Once you really know each flavor, you will have much more success at combining them into recipes. Start at a low percentage and work your way up. Many vendors provide recommended % ranges, and for others you can post a question in the DIY forum.
Start slow. Do not even think about making a large batch (>10 ml) of something until you know you will like it. What tastes like heaven to one person may be disgusting to someone else. At the same time, do not try to make your first mixes in really small amounts (<5 ml); the precision required to make those work requires a bit of skill that takes time to develop
Start slow. Download one or more of the calculator applications and practice with some imaginary recipes. That may generate some more questions you will want to have answered before your first mix.
Think about where you will do your mixing and how you will clean up, deal with potential spills, and generally avoid making yourself or others sick.
When you post questions on the ECF DIY forum, it can be helpful to make the thread title as specific as possible. There are many helpful people that don't have time to read and respond to every post, but if they see a thread title about something they have experience with, they will be more likely to chime in.
If you want help with a specific mix or recipe, include as much detail as possible: base nic concentration and PG/VG content; desired final nic concentration, PG/VG ratio, and volume (ml); and amounts of each flavoring and additive are all relevant. For the flavorings, mention the brand as well as the name of the flavor; there are a ton of RY4 flavorings, for example, and many of them bear little or no resemblance to each other.
Start hoarding empty e-juice bottles immediately. Sure you could buy them, but why?
Think about your motivation(s) for DIY-ing: Are you seriously trying to save money? Are you mostly concerned about health issues and want maximum control over what you vape? Are you looking for a creative hobby to play with? Are you a gourmet vaper that wants to create the most delicious juice ever? Maybe all of those things are true, but determining your priorities before diving in will probably save you time and money.
Steeping is not just for tea. Many flavors require steeping to develop properly, while some do not. The blogs linked below will tell you everything you need to know about that to get started.
You may well make a mix or two that is disgusting to you; don't sweat it. Learn and move on.
Regarding flavor percentages, it varies a lot with what you are using. One question often asked is, "How much flavoring should i use in my mixes?" Seriously, no one can abswer that question without knowing which flavorings you are asking about. Some need 15% or more, others are disgustingly strong at 5%. First resource is the place where you bought it and/or the manufacturer's website. See if they provide a recommended percentage range, then start at the low end and work your way up. The problem with too much flavoring is that sometimes that will make it taste less like what it is supposed to. Hoosier's blog (see link below) has a good flavor troubleshooting guide that explains the process.
The other resource for recommendations is the ECF DIY forum. There is a spreadsheet around somewhere with some recommendations for a whole bunch of flavorings, and you can get advice for many flavors by posting a question that includes the name(s) and brand(s) of the flavoring in the title. That will get you the most responses from people that have used them. But even then you may need to experiment a bit to find what works best for you, since taste is very subjective and what works for one person might not work for someone else.
Safety first; read these posts if you have not already done so (maybe read them again anyway). These will get you up to speed on what not to do:
These blogs were created by seasoned DIY veterans that have answered zillions of questions about the basics of DIY e-juice in this forum. This is the information they felt was useful enough to put into blog posts, instead of typing the same thing thousands of times:
E-Cigarette Forum - Hoosier - Blogs
E-Cigarette Forum - dannyv45 - Blogs
I also have a blog explaining some of the fundamental chemistry terms and concepts you may find useful.
(This is currently a work in progress, and feedback and questions are highly desired).
Many people with little or no chemistry training learn to DIY e-juice, but they must learn some chemistry to do it correctly, since making juice is practicing chemistry (so are cooking food and making mixed drinks, but DIY-ing requires a bit more specialized knowledge). Sure you could just start mixing things willy-nilly, but you would likely waste a bunch of ingredients and might make yourself sick. If you want to make good juice and vape it safely, understanding the chemistry and using consistent techniques will allow you to make recipes that you like a lot, and be able to recreate your successes and avoid repeating mistakes.
These terms should be well understood with regard to how they apply to DIY mixing:
Volume: for our purposes, volume is a measurement of how much space is occupied by a given amount of something. The most common volume measurement you will use is the milliliter (ml). Other volume measurements include gallons, liters, cubic feet, fluid ounces, etc.
Mass: mass is also a way of measuring an amount of something. The most common mass measurement for DIY is the milligram (mg). Other mass measurements include grams, kilograms, ounces and pounds. Note that ounces and pounds can also describe weight, which is not quite the same as mass, but an explanation of that is not needed for this discussion.
Concentration: this describes the strength, or relative amount, of a given substance in a mixture. The most common concentration measurements you will use for DIY are % and mg/ml. Note that many people and vendors just say "mg" when describing nicotine concentration, but that is not correct and can lead to some confusion.
Units: This is the way to express which measurement system you are using. Units commonly used for DIY include ml, mg, and %. No measurement description is complete unless the units are provided. If you ask me how much water to add to a mix and I say, "Four," that is not very helpful. If I say 4 ml, you know what I am talking about without guessing. Strive to always include proper units with any measurement you describe.
Solution: A solution is a liquid with more than one substance (a mixture). Unless you vape straight VG or PG, your juice will be a solution.
Ratio: A ratio describes how much of one thing there is compared to another thing. Ratios can be shown in different ways, for example 3 to 4 and 3:4. Percentages and fractions are actually ratios too, but they may be one sided; for example I can say that a mixture is 50% VG, or equivalently 1/2 VG, without specifying what the rest of the mixture is.
Dose: A specific, finite amount of something. For nicotine, if you vape 3 ml of juice that has 12 mg/ml nicotine, you have vaped 3 x 12=36 mg of nicotine, which is the dose you have consumed. How much your body has actually absorbed is another question entirely, and not needed for this discussion.
Dilution: Reducing the concentration of one or more substances in a solution. If you add PG, VG, water, and/or water to a nicotine base solution, you have diluted the nicotine concentration of the base solution.
So now we can describe a specific amount e-juice as a solution with a specific nicotine concentration and PG/VG ratio. We can also specify amounts of flavorings and any other ingredients, such as water, PGA, etc. For example, if I say I vaped 10 ml of 70PG/30VG e-juice (a solution) with a nicotine concentration of 12 mg/ml and 5% chocolate flavor, I have used a volume of e-juice (10 ml) at a specific PG/VG ratio (70/30) and flavoring concentration (6%), and I have received a dose of nicotine equal to 10 ml x 12 mg/ml = 120 mg (which is the mass of nicotine consumed). The units I used were ml, mg, and mg/ml. You can see that every concept defined in the list above is used to describe that 10 ml of e-juice. What about dilution? Yes, that is in there too, because the flavoring and nicotine base are diluted in the PG/VG solution.
The most common ingredients in e-juice are propylene glycol (PG), vegetable glycerine (VG), nicotine, and one or more flavorings. You could vape straight PG or VG, so everything else can be considered optional. Other commonly used ingredients include distilled water (DW), pure grain alcohol (PGA).
About nicotine base solutions: various nicotine concentrations are available, but 100 mg/ml should be considered a maximum for safe DIY-ing. You may be more comfortable starting with a lower concentration and that is fine, but anything higher than 100 mg/ml should be avoided. 100% nicotine is extremely dangerous and should only be handled by trained chemists in fully equipped laboratories. Note that 100 mg/ml is equivalent to 10% nicotine. Some people mistakenly describe 100 mg/ml as 100% nicotine, and that should set off alarm bells every time it happens.
Flavorings for vaping are normally flavor concentrates in a solution of PG, VG, and/or PGA. It is a mistake to assume that natural flavorings are always safer than artificial ones. Most of us prefer natural flavorings when we can use them, but not all natural flavorings are good for vaping. For example, any sugar (honey, molasses, agave syrup, etc.) is a natural flavoring, but if you put it into your juice, it will gunk up your coils quickly and is not a good thing to have in your lungs. Sometimes the line between "natural" and "artificial" flavorings is not distinct; stevia is a "natural" substance, but it is also an artificial sweetener, since it does not contain sugar. If you are seriously afraid of artificial flavors, I recommend trying unflavored e-juice. My main vape is 90% VG, 10% water, 33 mg/ml nicotine, nothing else.
There are additives which are used like flavorings, but are not flavors in and of themselves. Common additives include sweeteners, acetyl pyrazine (AP), and ethyl maltol (EM), but many other things have been used.
Separate names with a comma.