YES! This is a great way to make a "block" pattern, which is your basic pattern for fitting all pre-printed patterns. Find a pair of pants or a dress that fits great, and copy the seams onto pattern paper (I actually buy rolls of tracing paper from Dick Blick for this.)
It's going to be easiest with items of clothing that have simple seams and minimal tucks and darts. I think I got full instructions from a Nancy Zeiman book I got out of the library.
The basics: for areas that can be laid flat, you simply lay out the garment over paper and then trace the seam line by poking a pin though the garment into the paper every couple of inches. If an area can't be laid flat, fold it in half across that area and pin together. Trace out one half, (mark when the folded edge was), then flip, line up the folded edge, and trace out the other side. Tucks and darts can be a bit tricky at first, but practice makes perfect.
Be sure to add a seam allowance before you try to sew! The Palmer/Pletch fit books are great for learning how to make patterns fit, but if you get a flat pattern that fits perfect by tracing a favorite pair of pants then you can use that as a block for altering other patterns.