Buy fabric. Buy more fabric. Decide on dimensions, realize you don't have enough fabric, buy more fabric.
Cut 3 yd lengths of fabric into thirds lengthwise, hem. For table squares, cut into 20" squares.
They gave our tables the pop of color they needed, and since I didn't have to do the work, I say they were totally worth the effort. I think my mother-in-law and Mark's great aunt disagree, but they helped bring everything together and made up for our really low-key centerpieces.
Centerpieces by Ikea, all photos by Prema Photographic.
We didn't find out until two weeks before the wedding that we could use any table linens we wanted - we conceived of the table runners when we thought we had to go with white to be super-cheap. In retrospect, maybe we could have just gone with brightly colored tablecloths, but I don't think it would have had the same effect and I really loved the way they looked.