Sometimes, I press crease marks from point to point, then sew on the crease lines. This works pretty well.
A third method would be to use seam tape or some kind of 1/4" masking tape. The following picture shows what we mean:
|I tried to put tape on all three seams but this particular tape started to fall off before I could finish the seams. Though I love this tape, a different tape might work better for this technique. I sewed right next to one side of the tape.|