How thick is the juice you're using? If it's heavy on the VG, that might have something to do with it. I've been told (but haven't tried yet) that cutting the juice with small amount of distilled water will help if that's the case.
Honestly, though, I have found that I have to take a couple of priming puffs after every couple of vapes, as well. Since I've always used a 100% VG juice, it's something that I've been used to, so it's a habit at this point.
Have you tried taking a vape without letting it sit for a couple of minutes? One of my favorite aspects of the Raven tank is that I'm getting smooth, flavorful hits with no waiting. Even on my first fill, I filled the tank, dropped 3 drops in the center, and puffed immediately; I tasted nothing but my juice. If you don't have to wait, at least that takes care of what I consider the biggest annoyance of having to re-prime... when I want to vape, I want to vape!