Some years, I'm lucky, and the guy whose leaves I collect for compost will run them over with his lawnmower a few times to chop them up. We don't have a motorized mower so I can't do it myself.
If you have a mower, you can chop leaves with it, which, for me, are the majority of my compost pile.
I'm slightly tempted to get an electric mower simply for the leaf chopping.
I tried using a string trimmer in a barrel, but it wasn't very effective.