Work pass the burn. The true benefit of training comes from recognizing the difference between injury and soreness. It is common to feel like turning home after about 15-20 minutes initially but when you are totally winded and your legs feel like noodles, work past it with a good spinning cadence. Those days when you thought you could only do 15-20miles and you push it out to 30 or more are going to pay great divedends. You do need rest though. Also, do not forget proper nutrition. Throwing in a glutamine and brached chain amino acid mix to your water bottle will also decrease post workout soreness. Eat immediately after training with a fast absorbing protein and simple carbs. Creatine is great also. Good luck and hope that helps.