Read up on Waterbury's high frequency routines, as well as his
How To Make Your Own High Frequency Workout. He also has a recent one called 2x4, which has you do AM and
PM workouts twice a week.
As I understand it, the trick to getting away with high frequency is changing your set/rep parameters. But even then, I don't fully understand it.
For regular full-body workouts, I typically just go every other day until I feel like I need two days off. I'm lucky that I don't need to pay attention to what day of the week it is.