It depends, really. Sometimes I'm training for something (backpacking trip, 5K, or just focusing on building muscle) and sometimes I'm not. When I'm not, that's when I get lazy, because I don't have a goal to work towards. But even then, I do 2-3 cardio sessions (of about 30 min. each, stationary bike or elliptical) and at least one strength training session at the gym each week. With cardio, sometimes I'll do HIIT just to mix it up a bit. I also spend a lot of time outdoors hiking and riding bikes when the weather is nice, but that's not planned, I just do it because I have fun!
Right now I'm doing Couch to 5K, so that's three days a week of about 30 min. each on the treadmill. Plus at least one cross-training cardio session and one strength training session (I use the machines at the gym).
I usually do a short cardio session before strength training, only about 15-20 min., before strength training so I don't get burnt out like Ian mentioned, but I'm also only doing enough strength training right now to maintain my strength so it's not as much an issue for me.
When I was focusing on building strength, I cut out one of my cardio sessions and did 2-3 strength training sessions a week (one day upper, one day lower, and sometimes one day both).
I always do better if I make a goal in the monthly Exercise thread in the Challenge forum.
Also important to me? Doing something I ENJOY! Or working
towards something I enjoy and making a plan on how I'll get there. I really don't like doing strength training, but I
really liked being able to hike up that mountain in Colorado last summer, so that made it bearable.