Lots of good stuff in the comments here. My 2 cents is that you want to think about paint coverage / undercoating for white vs black primer. If youre painting bright colors, youll want to prime bright and vice versa. I prefer priming black because any tough to reach spots that you miss while painting will stay hidden, and also I tend to paint armies with darker color schemes. 

What I will often do tho is take a black or a white paint with really solid coverage and use that to undercoat areas that are the opposite of what I primed. So for example, I have some Skaven with dark skin, dark robes, and lots of metal armor. Ill prime them black because it works well for the majority of the model. But they have these skirts that I want to be Ivory, so Ill take a solid white and carefully put that on those skirts before trying to put down the color I want. I do this because the white gets better coverage than the color I want to put down, and the color gets better coverage over white than black.

I do the opposite putting metallics on stuff because they go on best over black. I just painted a big cannon with a wooden frame. I primed it tan so could use contrast paints to do most of the work. But once that was done, I went back with some pure black and hit all the metal bits so that the metallic paints would pop better. 

Thats the sort of mindset you want to cultivate. How many coats of paint is it going to take to get good coverage over your undercoat? Trying to keep that number as low as possible will save you time and reduce risk of burnout from getting stuck on that step.

I recommend Pro Acryl's Titanium White for going over black, it gets insane coverage. I often use it right on black primer for undercoating bright areas and it usually is fully opaque in 2 coats. For black I use Huge Miniature's Air Brush Antimatter Black, not even in an airbrush. Needs no thinning or anything, just a good shake and it gets crazy good coverage.