The nicotine strength you choose is mainly down to personal preference. If you've just quit smoking, then you may find the table below helpful when choosing what strength to buy. This applies to e-liquid, cartomizers (cigarette-style kits) and disposables:
Nicotine Strength (mg/ml)
You could also choose based on how many cigarettes per day you used to smoke, although you'll likely find yourself reducing the strength gradually as you get used to being smoke-free:
Cigarettes Per Day
Nicotine Strenth (mg/ml)
If you're using a Sub-Ohm kit or a Box Mod as opposed to a "pen-style" e-liquid kit, cartomizers or disposables, then we suggest reducing the amount of nicotine as these devices output a much greater amount of vapour - and therefore provide more nicotine per-puff. As a general rule, cut the amount of nicotine in half (e.g. if you're used to 12mg/ml, try 6mg/ml instead). This only applies to e-liquid.