I've done a couple this year and here are 3 other tips.
1. Make Sure you stretch your muscles from time to time, Calf Stretches, Back (cat Stretch), and Neck Stretches. Perform these every 20 to 30 minutes.
2. Some people Swear by Advil or Tylenol on rides. ( I haven't taken any while riding) But some people say that they couldn't survive without it. I do take some tylenol after the ride to help with muscle aches the next day
3. If the drive to the ride location is longer than an hour I would recommend driving with someone. Make your buddy drive, or take turns and drive 30 mins each. A long drive after a century can really suck if your by yourself.
One of the hardest things doing a century is being in that riding position for so many hours. If you are not use to it your body will definetely let you know. So just make sure you take care.
Have fun and Good Luck....