+1 to everything said above, with special emphasis on HTFU, drop bars or barends, lose the reddic wheels.
I would add:
-a decent gear ratio: i dont know what your running, but ~70 gear inches is generally best for longer distances.
-little breaks to stretch the legs: When I ride 50 milers fixed, I like to take a little break at 25 miles and at 40 miles to stretch the legs, munch on a cliff bar, refill the bottles, etc.
-stay fueled/hydrated. There are all sorts of articles on the amount of carbs and H2O you need to take in per hour. Google will find them for you. But the point is: eat food, drink water. If you are gonna be out 3+ hours, real food (ie NOT gels, energy bars, replacement drinks, etc) will help lots.
- Have fun, make your route scenic, soak in the experience. My fondest memories of rides are ALL of my longest rides.
But mostly HTFU. Boy scouts who never ride bikes rock 50 milers every year for a merit badge.