Ok
Fist thing is do a lot of homework. Nicotine can be dangerous. Get eye protection, a couple of kinds of measuring methods like a 1,5,10 cc syringe with a blunt needle works for me.
Here is a web site that has a damn good calculator. They have recipes and a good calculator to download.
eJuice Recipe Downloads
There are bunch of suppliers on here that sell the nicotine, PG,VG etc.
Go to the DIY liquid area and read the sticky notes.
When you start I would suggest using a tested recipe and then go from there.
Things to remember, Clean up very good, Don't leave the spills around. Wear gloves if you are working with like 100mg nicotine base. Wear the eye protection. I rubbed my eye once and had some juice on it and I will never forget that.
There is an online calculator also:
eJuice Recipe Calculator
In the DIY/Recipe area there are a ton of recipes.
I'm a relative newbie so I will leave it to the others for more and better advice.
Welcome aboard.