Things get tough when you start getting into the lower BF% but here are some tips that shoudl help alot:
* Continue to lift heavy weights. As long as you are using your muscles plenty, your body will be more reluctant to use muscle as fuel.
* Add Complexes to your training. For example: Do a power clean followed by a front squat and then a push press. repeat this for 4 sets of 10. Check out www.rosstraining.com
for other workouts like this.
* On cardio days do HIIT such as sprint 100 yards, jog back, rest as needed, repeat.
* Eat 6 meals a day with a protein source and a vegetable at every one of them. This will keep you in a positive nitrogen balance and keep you full. Avoid nonveggie carbs except for the meal after you workout.
* Post workout drink a whey protein shake and some gatorade or dextrose. You want a 2-1 or 1-1 ratio of carbs (from one of these 2 sources) to protein. This will keep you glycogen stores up and help you maintain your workouts.