I usually mix at 25%-35% flavoring -- high flavor mixes (thanks Bill's Magic Vapor!) taste good right when you mix them, none of that ridiculous steeping bidness, and great usually just a few hours later. You need creams and vanillas in equal proportion to the "main" flavor. Such as this:
Strawberries and Cream
Inawera Shisha Strawberry 16.0%
TFA DX Bavarian Cream 6.0%
TFA Vanilla Swirl 4.5%
CAP Sweet Cream 2.5%
TFA Sweetener 3.0%
It gunks coils within about 24-30 hrs of steady use, but the POW! of flavor is worth it.
Andria