After seeing my t-shirt quilt, my little sister brought round a bag of her old t-shirts and told me she wanted one for her Christmas present. She didn't really have enough t-shirts, so I had to cheat a bit and deviate from the traditional quilt technique. But actually it's turned out nicer than mine, so I'm considering an edit...
First grab your t-shirts and cut to size. This version took 24, 12"x12" panels from 12 t-shirts. I used the big design on the front, then also cut a plain design from the back. Some of these I left blank, but others I appliquéd on pictures I'd rescued from old knickers! You can do as you like, as long as you end up with the right number :)
Sew into four columns of six t-shirt panels. They should be one above the other NOT side by side.
Take care with colours - try to get a pattern going, or at least make sure to evenly distribute colours. Whatever you think looks nice really.
Sew each column together side by side. This should create a big sheet of panels, six rows (up/down) by four columns(left/right). It measures approx 72"x48", or actually a bit less because of the seam allowance.
Hew around the edge of your big sheet to make it nice and neat.
Finally, sew your sheet onto your fleece blanket, taking care to centre it and pin it carefully first.