It's often helpful to cut fabric at the end of a project into a pre-cut shape (10x10, 5x5, 2.5x2.5, 2.5xWOF, 18x22, 9x11) so it's ready to use on future projects.
It would be easier to give advice if you have a particular design in mind, but in general, you want to either do similar values in different colors, or similar colors in different values. There are a lot of great online resources about color theory. Honestly, though, if you still have a very small stash, you may need to supplement it with yardage and/or some pre-cuts if you are wanting a scrappy look to your quilt. I am working on the Calico Gardens quilt & originally thought I would mostly use my own stash, but I saw how striking it was with many different fabrics & decided to go ahead & purchase the optional monthly FQ packs that my LQS put together for the class so I could have that scrappy look. I'm ending up with quite a bit of leftovers that I will eventually (when it's finished) trim down to standard sizes to use in future quilts.
Here's a free online calculator to figure out how much yardage you need to get a specific number of "pre-cut" sized pieces. Just type in the width of the fabric, size of the pieces you want & how many of each size you need.
http://www.quiltersparadiseesc.com/C...Calculator.php