Are you continuing to prime by taking "pre-fire" draws into the tank, and then slowwwllly moving up in wattage in say, 5 watt increments, taking long slow priming puffs as you go? Just letting the coil sit is often not enough, although yes, juice type (ratio of VG/PG) and terminal wattage will play a role. Most coils have wattage recommendations printed on the coil, and I tend to land on the lower side of the recommendation (if I even reach it). You may be surprised that you can get a satisfying vape at lower wattages, but what wattage are you reaching/aiming for? It may be too high, or simply lack of priming....
If you could post more specifics, that may be helpful.
Anna