Whenever I make a new pair of jeans, the first thing I stitch is the back pockets. Having the pockets done gives me a little mojo burst, which I need at the beginning of an involved project.
I don't have an embroidery machine, so I have to work a little harder to get my pockets symmetrical. Over the course of my last several pair of jeans, I've worked out a system that works for me. I thought I'd share it.
The first thing I do is trace the pocket pattern piece I'm using, then draw in the hem and seam allowances (if it has them). I copy this several times (on a regular copy machine/printer) to give me something to sketch on so that I can try out different design ideas in the space I'll actually have on the pocket. Once I've settled on a design, I flip it over and trace it backwards so that the two pockets are symmetrical. I used regular computer paper today, but the next step is easier if you trace it onto tissue paper.
Cut out your tracing on the cutting line and glue it onto your fabric with a glue stick. Just dab a little glue in the upper and lower allowances. You don't want it glued permanently, but you don't want it to shift around when you stitch. Wonder Tape would work too, but glue sticks are cheaper. Pins are acceptable, but may distort your design as you stitch.
Now stitch your design through the paper. Go slowly and sew accurately along the lines you drew.
That big fat jeans needle you should be using does a nice job of perforating the paper, so it is easy to remove from your design! Just pull gently, starting with the big pieces of paper. When you get to the little ones, tug on your pocket a little. Even non stretch denim will stretch a little on the bias, and this will help detach the paper from your stitching.
Now all that is left is to press down your hem allowance on top and topstitch it in place, then press under the allowances on the other sides and bottom of the pocket. Since you already traced out the pocket shape, you have a template you can use for pressing. Handy!