If I am going to do a matchy, matchy quilt. I pick out a print and try to match colors in that piece. Pick out at least three and can pick out a different color from that print for inner border and sometimes I use the same pieces for a couple more borders.
Now I am making more scrappy quilts. You can do a controlled scrappy by trying to get them to all go together, colorwise. You could do just a bunch of fabrics you like, they don't necessarily have to match.
Look at lots of quilt pictures and you should get the idea. You could also try to pick a quilt picture you like and try to match the colors in it.
I try not to use too many solids. I stay away from lines, plaids, etc. too hard to cut them straight unless you use scissors for cutting. That is too slow for me.