The whole premise behind cutting is that you want to keep yourself in a calorie-negative state so that fat stores are tapped into for energy. You are going to lose muscle to some degree no matter what--it's the game of minimizing that loss you want to play.
DIET:
At your bf%, I wouldn't go any further than say 300 calories below your maintenance caloric level. The deeper the deficit between your maintenance level and your dieting level, the more likely you are to rapidly lose muscle. Eat lots of protein, I'd say around 400g per day, and split it up over 6 meals. Kill all but quality carbs--hit the green veggies, sweet potatoes are good too. Get good fats like eating salads with olive oil or eating natural sources like salmon. At least once a week have a cheat day without totally overdoing it. As you diet, your metabolism WILL slow down making fat loss harder and harder as you get the bf% down. Throwing in a cheat day jump starts your body and lets you get back to burning those calories/fat.
SUPPLEMENTATION:
Keep taking in supps like your daily multi, extra antioxidants, BCAA's, ALA, creatine that will help with recovery and keep the catabolic losses to a minimum.
TRAINING:
Keep lifting heavy to continue stimulating muscles to respond with growth. It'll be next to impossible, but if your muscles are trying to grow in response to heavy workouts, then you have a fighting chance of holding on to what you have. Do cardio, but don't go nuts with it. If you can lose 1-2 lbs in a week with 2-3 cardio sessions, then don't do more than that. Ideally, it's better to separate your weight training and cardio sessions so that you don't deplete yourself to an extreme. But, I've done it both ways with success.
What I've just outlined is a must for natural bb's, and maybe less crucial, but still hugely advantageous for guys on cycle.
