Okay... like I've said many times, I'm no expert, but I've had several ask me my process and so here is how I do it.
1. Rough cut all the T-shirt designs leaving as much area around the design as possible.
2. Square up each T-shirt again leaving as much area around the design as possible, but making sure that the design is approx. center. They won't be square, some will be wider than other, some will be longer than others, etc, etc.
3. Use Fusible Interfacing to back all the T-shirt squares. I use Pellon Stacy SF101... I buy it by the bolt because it takes alot... you are completely covering the entire back of each T-shirt square created in #2...
Now the fun starts...
4. I get my graph paper out and draw a rectangle/square the size of the quilt I want to make. If you want to include you borders in the size, besure to draw those on as well. I use 1 square=2 inches.
5. Layout your T-shirt squares so the designs look pleasing to you.
6. Add the widths of the T-shirt designs for each row to be sure your not going past the width of your quilt.
a) Take your longest row and subtract that amount from the width of your quilt.
b) Divide that number by the number of rows you have in your quilt.
c) Take the whole number from that calculation and add it to the whole number of each T-shirt design in the widest row. That gives you an approx width for each row. There will need to be adjusting to get the exact width of each row, but that gives you a starting place.
d) Take the width of each row you determined in "c" and add them up. If they aren't the width of your quit yet, then subtract that amount from your quilt width. This will give you the amount you have to add to the rows yet.
e) Then check the exact width of each T-shirt design against the width you determined in "c" to be sure it will have enough design around the design. Add to the width of rows until you are at the exact measurement of your quilt width.
7. Repeat step 6 for each row for the length of the quilt. Now you should have a grid that shows the rows of the quilt and the size of each block in each row.
Then you start creating each block letting your creativity flow and have fun.
Always remember that you've left plenty of area around you designs so you can trim off some here and there off the designs to add piecing space for each block. I generally try to leave atleast 1" on all sides of the design.
Alot of times I'll share designs between blocks. Say I have 1-1/2 inches on the right side of one block and 1-1/2 inches on the left side of the block next to it. I'll add those together and make a block that is 3 inches and can be pieced in two halves, so that when they are put together, it looks like they were pieced in. I try to keep things in rows because, I don't like set-ins or half seams.
I know this all sounds confusing, which is why I don't publish this, because I can't explain it so that it is always clear to everyone. If you have problems, send me a message and I'll help all I can.
I keep all the designs I use in the quilts, so I can usually help out with designs if anyone sees a design they like in one of my quilts and wants to use it... I use alot of Carol Doaks paper-piecing designs in my quilts...