|This is a pretty old and basic tip, but since I used it tonight and don't see it posted anywhere I'll go ahead and put it up.
Keep a hand sewing needle threaded with a doubled thread with tails about 4 - 6 inches long by the sewing machine; when topstitching collar points (or any sharp corner, for that matter) and approaching the corner, run the (hand) needle through the very tip of the corner and pull the thread about 1/2 way through and just leave it there. Then, when the (machine) needle is pivoted at the corner point, grab both sets of thread tails (the needle end and the free end) and tug it gently as you sew so that the corner doesn't get hung up under the sewing machine needle. Once the presser foot is well past the corner, the needle and thread can just be pulled out and stuck back in the pin cushion until next time.
I would credit the source for this tip, but I can't remember where I learned it!