Keep the cardio level to a low level. I usually aim for 120 beats per minute or lower. Just enough to give you a good sweat after 10-15 mins and do the cardio for 40 mins or more.

Can you do leg workouts?

I ask this because I injured myself last year and kept on doing legs twice a week while doing cardio also. This kept me from loosing too much weight and my legs actually grew from this. I needed people to help me load up the leg press machine though.