Everyone will have a different mixing technique. There is no wrong order to assemble your ingredients. A few tips I have picked up and incorporated into my personal DIY regimen are:
-Bookmark and read the tutorials for an ejuice calculator. I like ejuicemeup.
-Have whatever recipe you will use ready. If you are making your own concoctions or tweaking other recipes you have found,take notes!!!
As I'm sure you have read, you may invent an absolutely delicious concoction and never be able to replicate it due to not having made detailed notations of your work.
-Mix on a flat uncluttered space ,without distraction .Have only the stuff you need for the recipe you are working on in front of you.If you are distracted in anyway(children,pets,spouse,telephone,whatever) you could at least lose your place and forget what you have added or at worst get very sick (or worse) if working with very high nicotine levels and double or triple nic amounts due to distraction.
-Develop your own system for the order you want to add ingredients .There is no right or wrong here. I set my stuff in front of me and as I use each ingredient,I put the cap on and set the bottle on an adjacent table. This is MY cue that I have already added said ingredient.
-Treat all your mixing stuff ,especially nicotine as hazardous i.e. absolutely make sure children , pets and for that matter anyone other than yourself cannot access as they probably have no tolerance to nicotine and become very ill or die from nicotine exposure.
Re-read that last one . It is not hyperbole.A personal tragedy is easily averted by being cautious. You can use a toolbox with a padlock or whatever you choose . Just be safe and have fun. I like to use syringes for repeatability though they aren't necessary per se.
In short, I just typed all that to say , yes ,just mix it up . That's really it. Anyone can do it . Just don't think it is easy to make great juice.
I mean, making juice is easy, making great juice is a lot of trial and error.