First.... decide on the pattern to determine the amount of fabric you will need.
Second .... determine your color scheme. There are several companies that produce fabric lines of harmonious fabrics that are great to choose from.
Here are some thoughts to consider:
Jelly rolls - great for scrappy, strip piecing
Fat Quarters - small quilts....small yardage needed or scrappy larger quilts
Yardage off the bolt - great for large size quilts --- and for building your stash with whatever is left over.
Happy quilting!!