I think i'd like to pick up biking. there are a few bike marathons that i'd like to ride in or just go by on myself. I've got an 18 speed bike, not brand new or anything but it goes. Tomorrows my day off work and i want to go for a long ride in the morning. How many miles should i aim for? What should i do before and after the bike ride? And how often? I want to build endurance as well. Thanks