~Build yourself an awesome and deep base. This usually takes years so be patient.
~Train consistently (nearly) every day.
~Be smart about recovering between workouts by maximizing sleep, nutrition, compression, massage, etc.
~Pay attention to how your body is responding to the training you are doing (HR, paces, power, mood, appetite, sleep, etc).
~Work yourself until your body tells you it needs a break (see signs above). The deeper your base and therefore the more fit you are, the longer/harder you will be able to go before your body will start rebelling. Less fit athletes will require more frequent unloading.
~Unload when its time.
~Reload when your body gives you the green light (ie HR is normal and power/desire is there).
By the way, that whole unloading thing is the bomb! I'm reloading now.
15 Weeks til IM Canada.