I was recruited onto an ultra "Reach the Beach - NH" team (an "ultra" team means a 6-person team) last September and I had a ball. Funny thing, I didn't even know such a race existed up until 2 days prior to the start of the event, so, while I didn't train for the event per-se, as the miles and legs ground on, I got stronger and stronger as many of my (younger) team-mates started fading (I was the oldest on our team by some 25 years). Our team leader told me as I was about to start the 25th leg (my 5th) that the training I'd done up to that point had, unwittingly, been perfect for such a relay event.
So, how did I train?
In April of last year I started running between 3 and 6 miles, 2 to 3 days per week, and then worked my way up to running every day by mid June. Once I got to a point where I could run say, 6 miles per day, 7 days per week, I started bumping the daily mileage; first to 7 miles per day, then 8 (which is about where I was for the RTB-NH event), then 10, and now it's more like at least ten; always remembering to keeping my pace slow.