This is a tricky one and so personal. I know I've been teaching and a student has selected fabrics and I've secretly thought 'hmmm' - and then when the piece is finished it looks fab!
I think the easiest thing is to choose a focus fabric print and then pick three colours from that - which all sit together nicely. Once you have your 3 colours plus you focus you can build.
Take each one of the three colours at a time and find a couple of other fabrics in the same colour family that look nice with it. Chose lights and darks for tonal contrast. You will then quickly have 10 fabrics to pick from. You can add more or take some away.
I do think this is a learnt thing and you get better at it the more you do. Remember a good range of tonal value from light to dark is as important (or maybe more important) thank the actual colours or prints. Be brave and just cut. I often cut a piece and then substitute something else.
And have fun don't agonise!