How can I trace a pattern from a top with darts? I have a RTW (ready-to-wear, aka store-bought) dress which fits me well, and I'd like to sew a copy of it. I've done this before with loosely fitted tops, like t-shirts which only have minimal shaping, by doing a "rubbing" - lying the garment flat, tracing the seams on to tissue paper, and using that as a pattern base.

The bodice of this dress has darts on the side, so obviously lying it flat to trace will not work. I'm also concerned that the difference in stiffness between tissue paper and the dress fabric (a drapey knit) will cause inaccuracies if I try to e.g. make creases in the paper until it "looks right". I don't want to pick the seams of the dress and take it apart.

Is there a good technique to trace the piece with the dart? Or, how can I reverse-engineer how much of an angle was used for the dart? I do have a dress form, so answers which involve that are welcome!
If the dress is ready for replacement, you can remove the seams. You don't have to remove all of them, just the ones so the fabric can be layed down flat. I wouldn't recommend removing seams if you still want to wear the dress.

Another option is measuring: draw the pieces of your dress on paper as good as you can. Cut them out. Then put on your dress and see if the pieces you've cut out of paper, cover your dress. If you've done well, you'll also have the dart on the right place. When the doesn't fit correctly yet, cut off what's too large and add paper where your pattern is too smal. You can just attach a strip of paper with some tape, no need to redo the whole piece.

If all else fails, you could try to find a pre-made pattern that resembles your dress, and maybe adjust some parts (e.g. length, neckline).