I've copied a couple RTW garments now, using a few different methods, but I tried something different on Jeff's shirt that worked really well. And it uses a cool sewing gadget, which I feel deserves extra points. It's always gratifying when you find a real use for some notion you bought months ago that you just had to have.
This is a Clover serrated tracing wheel, it has spikes instead of a smooth or bumpy wheel. I think it's supposed to be for tracing around a pattern onto another piece of paper, on a soft surface the spikes penetrate leaving little holes in the shape you traced.
However, I found that by placing a roll of pattern tracing cloth down on my ironing board, and pinning the shirt in sections on top of that, I could use the tracing wheel to mark the seamlines. Even though the wheel doesn't penetrate the shirt, it left a very clear marking, and around the hems you can trace directly onto the cloth, which makes nice little holes. I'm sure this would work equally well with paper too. I found sticking the pins straight down through the ironing board (in between the metal mesh) worked the best for holding the fabric taut and staying out of the way of the tracing wheel. You have to press down fairly hard on the shirt with the tracing wheel, but with a tightly woven material like this it didn't disturb the fabric at all. I will have to experiment with more delicate fabrics to see if this will work.
This method works best on uncomplicated garment sections, especially those that can be laid completely flat like a shirt. Darts and gathers require other methods, but most other pieces can be copied easily. Even if a section can't be laid flat, you can copy it in stages, pinning as much as you can flat and then lining up the rest after copying the first part. This is how I copied the sleeves, and it works for princess seams too. Remember to leave enough room around the pattern to add seam allowances.