One of the shirt had a really neat saying on it.."If you can imagine it, you can acheive it. If you can dream it, you can become it." I cut it apart and put it in the sashing strips and staggered them down the quilt. I try to use as many components and things off the T-shirts as I can. I cut off pocket logos, the sleeves, everything. I'll cut the basic T-shirt square (I use a 12 1/2" square up ruler) and then start adding things on top of the blocks and sometimes going into the sashings. I know some that will measure every T-shirt and graph it out, but I prefer this method and since I teach this class, it's a lot easier for beginning quilters to accomplish.
Another thing that beginner's struggle with is making the sashings line up if there are no cornerstones (little blocks in the sashings between rows). To avoid having your sashings not appear to be in line: Lay your row with the sashing right side down. Lay a ruler on the seam line, extending the ruler through the sashing and mark. When you add your next row of T-shirts, match the T-shirt/sashing seam with the mark on the long sashing and pin.