Just lurking this forum was invaluable when I was working toward my first century. Thanks again everyone.
Training for a new rider - Long slow distance had great immediate benefits for me. I got serious about a century after my first 50mi ride and did my first century 8 weeks later. Doing 2 or 3 weekly steady and easy endurance rides of 3hrs both was good for fitness and learning about what HR is telling you. Use HR to gauge effort on the century ride.
Distance - The 1.5x rule about going half as far as your previous distance works, once you've done a metric or a little further, plan to do the century. If just doing it on your own don't lock in "a day" for the event, take advantage of the fact that you just want to get it done at some point in the season (basically, try not to think about it ahead of time.)
Sunscreen - I applied sunscreen every couple hours to my arms and thighs. Ended up with a burnt back, complete with outline of the jersey tag. Wear a protective base layer that has some sun protection, and has the added bonus of making you more visible. (this may cause you to tan in "gloves" while your arms are protected... haven't figured that one out yet)
Nutrition - whatever works for you, but it's obviously critical for this duration, less is more IMO so guarantee a good base with manufactured stuff (gels and powders are efficient) and snack along the way - salted almonds and apricots are often mentioned and work. Enjoy the stuff sold in the checkout aisle, just don't overeat.
The route - Have a "big" checkpoint, e.g. know a few places you can stop for food/water at 55-75 miles (this is the point of no return area if following the distance rule of 1.5x.) Restock and know that you're only 25-45 from finishing. Know the end of your route well if possible too - the last 20mi are a bit mental, but if it's well known to you it'll be just like starting a new ride (just already really tired!) If it's a segment you've done countless times that's a get out of jail free against any doubt you won't finish.
Data - Get an app on your phone, record the ride, a line on a map is the quickest way to show friends what you're talking about, and a great reminder that you did it while you're waiting in line for whatever.
Repeat - After the first is done think about another - your fitness is great, and the unknown century is now known, so keep up some training and try to get another one in within the next 4/8 weeks. Use the days you already had planned out in case the first try didn't work.
Oatmeal cream pies - I can't find the thread now, but certainly one of the most enjoyable century stories on BF. Search for it.