Don’t mix e-liquid after having enjoyed too much of the adult beverage of your choice. Once I was mixing e-liquid after having had a few too many drinks, and almost mistook my nicotine bottle for my VG bottle. What a disaster that would have been.
Don’t rely on cheap plastic pipettes for precise measurements if you’re making a small batch of e-liquid - it’s really hard to get an accurate amount. Use syringes instead. Plus they can be cleaned of residual flavor more easily than pipettes, which always seem to “lock in” whatever flavor you’ve used in them.
Don’t sweat it if your first trial of a recipe isn’t just the way you want it. Unless you make your living by making and selling e-liquid, either only you, or else just you and close friends, are going to be trying it, so it’s not a disaster if it doesn’t turn out perfectly. I’m sure we’ve all made meals in our kitchens that didn’t turn out quite how we wanted; that doesn’t mean they were inedible. Just learn from your mistakes and move on.
Don’t let it get complicated to the point where it’s frustrating - DIY vaping is supposed to be an enjoyable hobby, not a full-time job.
A few “do’s”:
If you’ve got a bottle of nicotine you know you’re not going to use for a while, store it in the freezer - it’ll slow down the oxidizing.
Make the minor investment in one of those little electric e-liquid hand mixers that use a AA battery - you can get as much mixing in a minute as you get in an hour (or more) of shaking by hand. For a 15 ml batch I mix in a 50 ml beaker; for a 30 or 50 ml batch I mix in a 100 ml beaker.
After decanting into the bottle, set the bottle in a cup of very hot water (before applying your label, of course), and let it sit until the bottle is cool. Repeat if desired. Then dry the bottle, apply your label, and store. The steeping time will be greatly reduced.
For greatest accuracy, use appropriately sized syringes for measuring - if you need 0.7 ml of a flavor, use a 1 ml syringe, if you need 2.3 ml of a flavor, use a 3 ml syringe, and so on. You don’t want to try measure out 0.7 ml of flavor into a 10 ml graduated cylinder. I use the cylinders for measuring out my VG, which makes up the bulk of my recipes . . . plus, it’s a lot of work to try to pull VG up into a syringe, since it’s so thick.
Ignore the “single use only” statement on the syringes. They’re intended for medical use, where single-use is obviously appropriate. But for our purposes, they can be cleaned and reused indefinitely, until the measurement numbers begin to wear off, at which point it needs to be replaced.
You need to wear rubber gloves when handling nicotine, especially at higher concentrations, but I’ve seen a lot of tutorials where the person wears gloves, handles nicotine, spills some nicotine on the gloves, and continues with the rest of the recipe while wearing those same gloves. This defeats the purpose of avoiding cross-contamination. What I do is to put on my gloves, add my nicotine first, then carefully remove the gloves and discard. The next step is to add my VG, the bulk of the recipe, since that dilutes the nicotine down to a level where it’s not so dangerous if you happen to have some skin contact with it, and you can always wash your hands.
Prepare ahead of time! Make sure you have your recipe handy, and gather together all the equipment you’re going to need. You need to be able to concentrate on what you’re doing when making e-liquid, and you don’t want to get halfway through making a recipe only to have to stop what you’re doing and go digging around through your stash trying to find a funnel, a syringe, a beaker, an ingredient, or whatever. Figure out what you’re going to need before you start.
Use a steady hand when drawing up a flavoring into a syringe - it’s all too easy to spill that stuff, and not only is that a waste of money, your kitchen (or wherever) is going to be smelling like whatever flavor it was for a long time.
Finally, get involved in forums such as this one, as well as vaping advocacy groups, and above all, if you vape in public, don’t be a douchebag about it.