Sorry I'm just now posting them! My instructions to go with the pics are probably going to be 'lacking'. Hopefully you'll get the ideal of what I'm doing from the pictures though. I find writing instructions very hard... maybe I should do a video and post it on youtube!
After much reading and researching different ways to copy RTW and make patterns this is the easiest I've come up with... and gets me the best fit. So far I have used this method to copy a pair of rtw yoga pants, 3 different pairs of jeans and a long sleeve knit top.
I use cheap non fusible interfacing for my pattern. Its strong and sheer.
I do this on a carpeted floor so when its all smoothed out and flat I stick the pin straight down into the garment and in the floor. This holds everything nice and tight!
After all traced I measure different fit 'points' and compare them to the measurements of the rtw garment and "true up" my lines.
I measure the fly pieces and make them according to the measurements.
I lay the interfacing on top of the pants and trace along the fly top stitching. This makes my fly template.
I lay the cut out pattern piece on top of the pants to mark where the pockets go