It's a process for me. First, I choose 3 or 4 fabrics that I like together. (I'm 'color challenged', so don't use many fabrics in a quilt.) Then, somehow, I get inspired, and it goes from there.
I love to use panels as the start of a quilt, then play with how to border them. I've also cut panels into blocks and then 'found' the right way to make them into a quilt. Big print fabrics are also great to design around, especially since I like big block quilts.
Recently purchased EQ7, so now I can test my ideas in the software. I like it, and it tempts my brain to do more complex quilts. It also lets me turn the blocks to come up with unique quilt patterns.
My favorite shape for piecing a quilt top is squares and rectangles. It's amazing how those two shapes can be used to create a quilt top.
One fun thing I do to test blocks is make doll quilts. If the doll quilt looks good, then I can make the quilt. I donate the doll quilts to 'Fostering Hope', a private organization that provides clothing, toys, toiletries, etc. to children taken into the foster care system. Everyone wins - can't beat that.