As soon as you start, have your section meet, introduce eachother, maybe tell something unique about themeselves or something along those lines to get everyone familiar with eachother.
I'd suggest something along the lines of starting off the year with a party or get together, and making everyone feel welcome, especailly the freshman! NOT AN INITIATION! What we did, we (drumline seniors), called each of the kids parents, and asked if it would be fine to take everyone out to one of our houses, which happened to be out in the country, and had really fun games and bonding activites, ordered pizza, ect. We blind folded them after rehersal, made them think they were in trouble, and took them out there. We had a blast. We were done at 9, so it doesn't have to be a super late sketchy type thing.
After this just have regular meetings, make sure there's nothing bad going on, have a cool section shirt, and just be involved. One of the most benefical things was just making sure we didn't have any issues with eachother, and if we did, we solved them.
One of the most fun things we did was bowling night.