early start so that dwindling sunlight is one less reason to shortcut/pull the plug on the century attempt.
if you do it right, you should have 50+ miles under your belt before noon.
a flattish century is waay easier than a hilly/mountainous one.
have usually schedded a fave lunch place enroute in the 40-60 miles ridden zone (to have something to look forward to in the first half) altho did it at the 92 miles ridden point once.
as mentioned elsewhere, scenery is a great companion on the journey. helps to have roads that pull you along to see what's around the next bend.
if it's going to be a mountainous/ hilly century, try to knock out the hardest/longest climb first.
if you have a chance to ride segments beforehand, do it. especially the hardest projected stretch. at least drive it slowly.

once you've got a few under your belt, you can mess around and see what works best for you with calorie intake, scenery, altitude gained, prevailing winds, road quality, et al.