I think that you need to find the most pleasant combination between volts from your pv and ohms from your cartos/atoms. Get an ego twist so you can have pretty good changes with a very reasonable price... That's where I started when i wasn't satisfied with VTF from my liquids and device. Proportion between pg and vg is a very important thing too: i bought a bottle of pg, one of vg and some flavors I supposed to like, I started mixing and I found my personal proportion which I can now easily buy too from ready-made liquids... (I buy elit liquids but they are only available here in Italy)
Hope it helped a bit!
Hope it helped a bit!