if you are going to put batting in your t-shirt quilt be sure to buy one that says on the packaging that is works for tied quilts.
then the rule of thumb is to place your ties every 4" or fist width apart, meaning if you put your fist on any spot there is a tie above, below and to each side of your fist. start in the center and work out and around. use a sharp needle (an embroidery needle has a large enough eye for the perle cotton to be used and is sharp enough to go through the knit t-shirt fabrics. when i tie a large quilt i still baste really well, but i do not know if other people do or not. i get together with a little sewing group when i can fit it in my schedule and they are very inventive. when they want to tie a large quilt they use chairs (folding metal) and clamps...they set the chairs in a square, backs out, seats facing in, the size of the quilt back, then they clamp the quilt backing to the backs of the chairs along one end; then they pull it taut and wrinkle free and clamp the other end, then go to one side, then the other...oh and they do leave an escape hatch :) (one missing chair) so someone can get under the quilt. it is really fun to be part of this activity and they tie a quilt in just an hour or so. one person underneith, however many on top...needles with perle cotton are pushed down through the underneith person sends it back up (this is only done if it is a big quilt where reaching is impossible to handle the top and bottom.