Originally Posted by Lazybones
You get seven total at Amazon, right?
I find I can usually come up with 3-5 solid tags pretty easily, so you could cover the common ones and use the rest to be more specific/unusual.
I just looked and I have 14 on my first book presently. I personally would put BOTH a few very common ones, and a few very specific ones. That way you get exposure in both groups.