I used an iron-on tricot stabilizer. Yes, you adhere the stabilizer before you cut the blocks from the shirts (you can cut the front off and just iron the stabilizer behind the area you want to use, then square up for the block). Be sure to put the stretch of the stabilizer perpendicular to the stretch of the shirt. I've only done 2 t-shirt quilts, but I did a rather loose meander on the shirts themselves because some of them had those plasticky letters and logos that I didn't want to quilt over. By meandering I could go around those areas.