A lot of good advise was already given. One other thing to be prepared for it a flat tire. Take along a spare tube, patch kit, tire tools, and a pump! I have seen too many people who, appear to be new to cycling, walking their bikes along the path with a flat tire. I also suggest taking a cell phone, some money and an ID just in case.
As the others said, don't worry about cadence and other things until you get comfortable with the bike, reaching down for your water bottle, and knowing when to turn around. Also, remember you are out to have fun and get a little exercise while having fun!
I guess I had more than 'one more thing' to day....
