|I was looking at my Burda WOF pattern sheet in dismay, as I wanted to make my standard alterations while tracing, but moving back and forth between 3 sizes was confusing me. I didn't want to write on the pattern sheet because of show-through on the other side.
I found that brightly colored post it flags, shaped like arrows with black outlines, could "point" to the correct cutting line and guide me while tracing. While these flags are highly visible through the tracing paper, I think any Post it-type product with a mark to help orient you would do the trick.
Best of all - they leave no residue, and they are reusable many times.