Train, always train. Cadence training, you need to be able to spin and keep a constant speed for sometime, it takes at least a month or two to actually prepare for this.
Padded cycling shorts, yes, they look gay, but if you are gonna ride more than 60km, you'll need it, unless you have those massive lady saddles, then you'll end up chaffing your thighs.
Just train, ensure you can ride 50+km one day, then get up and ride again the next. I used to cycle thursdays, fridays, sat and sundays. I'd join this if i had a bicycle next year. I have a frame, fork, stem and handlebar, and front brake, cranks and a 9 speed shifter.