It just varies person to person. Back before all the high wattage stuff we'd say 24mg for a high volume smoker, 12mg for a PAD smoker. But I've seen 3 PAD smokers get along fine with 12 and single PAD smokers need 24? I use 36mg on everything I own, low and high watt, but I'm certainly not the norm. Most seem to think in a sub ohm vape 6mg is a good place to start.
I'd suggest you first find a juice you like, then get some small bottles made up in different strengths to see where your body wants to be. Then try that for a while, and ween down as you need to.