I use a sock on my iron and when I'm doing a patch I run the iron just a little hotter than normal. I set my iron at 250 degrees with the sock.
I lay the patch on, lay the iron very gently on it, let it sit for a second, and then move slowly from center to end, pick up iron and go back to center and out the other end.

On this first pass I hold some of the weight of the iron off of the patch and move slowly. After the initial passes, I run the iron slowly over it again moving slowly and
let the weight of the iron do the work.

Slow and light, work from center out.