In an attempt to be useful for once, I've made a tutorial of the method I use to make a pattern from an existing garment, for when I'm too lazy to make my own pattern.
I like to think I invented this, but it's also highly possible everyone uses this method but never told me.
Step 1: Place a large sheet of newspaper on the carpet, then put your (inside-out) garment on top of that, laying it out so the piece you want to copy is as flat as you can get it.
Step 2: Using long pins at 1-inch intervals, pin down all layers on the lines of stitching of the seams, stabbing right into the carpet (god, I speak the good english, but I hope you get the idea).
Step 3: Ease the garment up the pins, and with a marker pen, draw lines between the pins. Alternatively, you could just whip the whole lot off and play dot-to-dot with the pinholes, but I like being able to slide the garment down again and check that the line I've made is accurate.
Step 4: Take the pins out, then draw a second line around the pattern piece for your seam allowance (usually 1.5cms), and cut on this line.
Lather, rinse, repeat for the rest of the pattern pieces, making allowances for darts and other such nasty tricksy things.
Hope this helps at least one person.