Like Jeanne S and SuzzyQ have said your stash will build on it's own, so concentrate on one quilt at a time is my suggestion. When I started over 20 years ago I really had no idea what I liked. I went to the fabric store after making a small table topper of 3 safe fabrics (basic blue, pink and white background) and started buying several fabrics just because I liked them. Some of them I still have and they don't excite me anymore so I'm trying to use them up in scrap quilts. Trust us, your stash will grow with just the extra fabrics from the quilts you make one by one. You'll be surprised how quickly this will happen.
You can also do the thrift store thing, but you are still paying for fabric and for me to spend money on fabric I have to really like it/know what I want to do with it these days. I don't shop willy nilly like that because quality does matter if you want to have the quilts you make for others last more than 5 minutes.
I also don't recommend telling people you would love fabric for gifts. My husband and son love to buy me fabric, bless their hearts, but their likes are not always my likes and much of what they have picked out are still sitting in my stash unused. And who says it will go with what I do like and end up buying in spite of their choices for me.
So just find a project you are excited about and buy for that project (adding a little extra if you really love the fabric knowing you will probably use it). Believe me your stash will come.