From my own experience;
Start off at a nice leisurely pace definately, find a speed and rymthm you can sustain quite comfortably without breaking a sweat, relax into it and tuck the first 20-30 miles away without really noticing you've done them. If you do get a climb fairly early on, do not attack it, dont be afraid to spin up it. My first century was a jump from regularish 50 milers, I got cocky and set quite a high pace at the start and was quite aggressive on my first three climbs. Of course, I felt great to begin with, but the final 25 miles were simply hell to the point that when I'd finished - and for a while after - I honestly wondered whether I wanted to go through that again. I've done two more centuries since using the "dont start until the 2nd 3rd strategy" and been fine.
Hip's tips on food seem bang on.
As has been alluded to aswell, know your route. LBS' for spares, food resupplying, hell even transportation options if the absolute worst should happen, but more than that I found it helps in the mind to know which landmarks your going to pass along the way, be it villages, towns, or actual landmarks, so in your mind you can break the ride down into more manageable bitsize chunks; Personally, at the 70 mile mark, I prefer to be "aiming" for the next village 5 miles up the road rather than concentrating on the fact that Im still 30 miles from home!
What are your normal distances currently anyway?