Basically you never should have two hard riding days in a row... So if you do intervals on one day, the next you should be riding very slow (with a beginning friend for example!!!) or not at all. So for example your commute should be as relaxing as possible on days after a ride.

I have a a few Bicycling Magazine books (mostly edited by Ed Pavelka I think) that cover this topic. I think they are must-have for beginning cyclists!