My tips-
Use a decent calculator
Take notes
Measure precisely
Start small - you can get larger bottles of pg, vg, and nic, but buy sample sizes of flavors until you know what you like.
And mix small test batches of everything. 5-10 mls is plenty to try something out. And you’ll find, some recipes will stay good for months, so you’ll be able to make large batches once you have the recipe how you like it. Other stuff will fade or go weird on you, and you’ll stick to amounts you can vape before it doesn’t taste good.
I did single flavor tests of everything, so that I knew how it would be in a recipe- I still do if I’m not familiar with a flavor. There’s a big difference between brands, and some just will not taste right to you. You can’t make a bad flavor good.
Keep your nic in the freezer until you use it, then give it plenty of time to come to room temperature.
Keep your flavors in a cool, dark, dry area. Juice, too.
And ask if you’re uncertain. The diy is very helpful.