Hi Tom. Welcome to the QB, you asked a great question (and it's the same one I had when I first started quilting). And now you're going to get a lot of different answers, from each of us (then you will get to try the ones that sound good to you, then when someone asks this question down the road your answer with be among the list too
).
I found that I would see all of these great colors, but I couldn't get them to work together because I had so many (I was picking up each color I liked and everything I liked, so I was all over the place). So I found a pattern (I used a simple rail fence pattern). I decided on one print fabric (this became my focus fabris and was a medium sized print, it was a bright green background with different colored dots that also had a black outline around each dot), this became my starting point. I went on to pick out four fabrics in soled colors (that went with some of the dots on my focus - for me just finding a focus fabric to start with was enough for on day, my mind was swimming), so I kept my fabric in a bag in my car so that the next time I went to town I could look for blenders).
This is how I start most of my quilts still, even if I don't have a pattern picked out. I be thinking of starting a new quilt, so I will pick out a focus print that I just like (I also have to feel I can cut it up). I will keep it and start to pick up blenders (other fabrics), to go with it (most of the time I will use more than one print in a quilt, but I will work with a theme in mind from my focus fabric). I spent two years picking up fabric with stars on it (I would get half yard cuts, if I liked the stars on the fabric), didn't know what pattern I would be using (and I ended up with a lot of stars). When I did make my quilt I did end up with a lot left over, but I was able to pick the colors out that I wanted to work with (then used the left overs on other quilts).
Good luck, and remember NO rules just FUN.