How good do I need to make my primer coat?
I find that primer dries so fast that you have to do the job quickly, but it's worth it in the long run to get it somewhat even: any time saved by doing a poor job of priming will be more than made up for trying to get the finish coats looking good.  

The primer coat doesn't have to be perfect, but it should cover the surface (no bare spots) and it shouldn't be so blotchy that you get drips or visible unevenness.