I typically try to go to the gym everyday if possible. Or if my schedule and time constraints get a bit too hectic, I still try to go at least 3 or 4 times in a week.
And I try to burn at least 45 minutes each time I go. And if not, I take a short-cut with only 30 minutes or so.
I used to struggle a lot with maintaining this goal due to laziness in general. But then I finally kicked myself to stop acting like this.