Hi sedgeez. I, like Nemia, tend to prefer linear readings, but usually go with an odd number of cards, 3, 5 and 7 are where I usually go. I've found a lot of spreads on A.T. as well as many other resources now which often fit my needs. When one doesn't quite fit, I'll simply alter it - usually just by changing the positional meanings. Thus a "issue-blockage-advice" 3-card spread, has become an "issue-blockage-contemplate". Or, creating my own 5-card Focusing Cross, based off of several others that I had found.
Basically, what I'll do is first figure out what questions I want answered, as Nemia said, that gives you a good idea of how many cards you're going to want to use. Then ask; will a simple linear spread work ("a" leads to "b", to "c", etc.), or do you need to look at more complex relationships (how "a" affects "b" and how "d" affects "a" and "b" or whatever you need). I created one several years ago in a 3x3 grid, so you were looking at multiple affects across multiple ideas (past-present-future/mind-body-spirit). Then too, a few days ago I created one for a question one friend asked me - but when I started thinking about it, I felt the "energy" of a simple linear wasn't enough and ended up doing a spiral.
I haven't looked at the books that others have mentioned, though I am now seriously thinking about it. I have looked at some web sites and seen a lot of spreads that people have posted here. I will add, that once you do start creating your own spreads ... it opens up all kinds of new possibilities.