Having a simple harness helps. The first harness I purchased for Max was one of the thin, strappy ones with 2 snaps. I don't think we were ever successful putting it on him.
I purchased a simpler style that went over the head and had one snap, similar to this one:
Just Pucci Puppia Soft Harness
Much easier to put on a pup. Once it was on, I distracted Max with toys and treats. Didn't take him long to forget he was wearing something new.