I'm by no means an expert on gar fishing but I can offer a little knowledge. I mainly target catfish and catch a lot of gar by accident.
My suggestion on bait would be to catch yourself some carp and cut it into big chunks. Bluegill, drum, buffalo or other types of cut bait would work as well.
Get yourself some big treble hooks. The specific setup you use would depend on how you are fishing. A different setup would be needed for bank fishing vs boat fishing.
One thing to remember, gar like to swim away with their prey before they actually eat it. So don't try and set the hook as soon as you get some action. Let them run with it for 30-60 seconds, then set the $#!# out of it.