I work out with a personal trainer.
I have 1 hour training with him every 2 weeks. Inbetween he sends me workouts to do "on demand": I tell him when I am likely to go to the gym, and he emails me what to do then.
I try to get in 2 to 3 workouts per week, plus go swimming once a week, and during summer I went rollerblading during weekend whenever I had time and the weather was fine. This won't be possible soon anymore :-(
I'm not fixed on days or classes, nor on a number of sessions. I plan around my life: more busy = less workout; more time= more workout. And I try to not have gym sessions 2 days in a row.