I have done several T-shirt quilts and quilted on my domestic sewing machine. I usually stabalize the quilt sandwich by stiching in the ditch. Then I go back and quilt the blocks. I have used both invisible thread in the top and a varigated thread. I stitch various background designs in each block (meandering, echo quilting, vines and leaves , waves etc.). I will usully outline the block design and sometimes stitch within the design itself (lines of a basketball, around letters, etc). When stitiching in the design itself, the key is to go slow. The design itself sometimes has a tendency to grab your needle.
Here is alink to one of the ones I have done.
http://www.quiltingboard.com/main-f1...ml#post4790296