These guys above me pretty much nailed it, but here's my 2 cents.
Wicking material, wicking position, and airflow are the main factors.
I find that Japanese cotton has the best flavor, but I know other people prefer different things like silica, regular organic cotton, cotton gauze, etc.
I'd also drop the nic down to about 8mg if you are at 18-24 right now. I use 12mg in my kafuns and foggers, but with dripping I use 6mg.
Best of luck!