For me I started simple, I wanted a basic
tobacco. For that I use Seedman Commercial flavoring and a bit of Tobacco Absolute diluted (available at multiple places, "diluted" means it is TA cut with 50% pure grain alcohol, though a high proof vodka could also be used).
Got a couple of oral syringes from a local pharmacy -- they gave them to me free, just asked at the desk. 3ml or 5 ml are nice -- markings are every 0.2 ml.
You'll need pure VG USP, and likely pure PG USP. The VG can be picked up at just about any pharmacy -- ask at the desk, it might well say something like "Glycerin USP"; mine was labeled "Skin Protectant", but the ingredient list showed exactly one thing, glycerin (99.5%) anhydrous, which is appropriate (higher % is also okay).
Mixing -- a small, clean, area. I have a work area in my basement, store all my bulk stuff in some cheap plastic organizers.
Yup, it is simple. Pick a desired final mg/ml strength, and that tells you how much nic liquid to use. For instance, I have 60 mg/ml, and want to make a batch of 10ml at 24 mg strength. 24x10 = 240 mg, so I want 240/60 = 4 ml of the nic liquid. Put 4 ml in the bottle.
A general % flavoring, at least for simple mixes, is 10 - 15% of a flavoring. For my Seedman Commercial I use 15%. .15x10 = 1.5 ml of the flavoring goes in the bottle.
I've used up 4 + 1.5 = 5.5 ml. pretty common mix is about 80% PG, 20% VG. 0.2 x 10 = 2 ml of VG goes in the bottle.
I'm at 7.5 ml, can add 2.5 ml more of plain PG, or maybe 2 ml PG and 0.5 ml of 160 proof vodka (since you can't buy PGA in NY).
I've now got 10 ml of 24 mg strength tobacco liquid. I add 4 drops of TA diluted per 10 ml of liquid to firm up the flavor, slightly enhance the throat hit that I perceive. This is drops, only about 0.1 ml -- try adding just one or two drops, shake the whole thing up, vape it; if you want it stronger, just add another 1 or 2 drops, shake and vape.
Be careful on keeping things clean, any spills, etc. 60 mg strength nic liquid doesn't bother me, but many people, as well as children and pets, are much more sensitive to it. Clean well, put unused liquids safely away, and enjoy!