Originally Posted by Ratcat
Lifting heavy and eating clean.
The same thing that built your muscle in the first place will keep it. There are no magical exercises. Just keep using the ones that work for you.
However, when you are in a caloric deficit, you will notice you are not able to recover as well from workouts. Thus volume may need to be reduced at times and I would caution you not to use failure often.
While I tend to disagree with Ratcat about using failure when cutting, I do agree with his thoughts on HIIT. Basically, most fat loss should occur with diet and you only want to start throwing in extra sessions (like HIIT) when you have stalled.