It's really hard to retain 100% of your lean muscle mass as you try to lose fat. Look at the people who are by far the most proficient people on the planet at doing so-- Bodybuilders. Those guys bulk up to the point that they almost look fat, just so they can have an overabundance of muscle to spare for when they diet down. In their whole diet phase, the name of the game is losing fat while sparing as much muscle as possible. They get paid a lot of money to do it, it's their main job, and still it's tough for them.
Diffrent people are going to have diffrent answers on the best way to do it. I think one thing we all can agree on is that you will need to keep your protein levels high in order to ensure that even after you cut calories your muscles are recieving all they protein they need to exist.
Here's my individual opinions on how to go about it.
You can either increase the amount of calories you burn during the day to put yourself into a calorie deficit, or you can just reduce the amount of calories you eat. One way has you working more, one way has you eating less.
If you choose to work more, that's usually were cadio comes in. There are lots of different views on the best types of cardio to do in a cutting phase. It gets sort of tricky, because like I said, it's all a matter of what type of cardio will burn fat without burning muscle.
I favor a slower, steadier cardio pace at approimately 50-80% of your max heart rate. For me, that equates to a really brisk walk which I do for about 30-60 minutes 4-5 times a week (when I'm cutting). The ideaology behind the slower, steady pace is that (theorically) while you're buring fewer calories, a higher percentage of the calories you do burn are coming from fat. If you buy into the theory, then sounds like a winner.
Furthermore, a lot of people prefer to do this typ of cardio first thing in the morningn on an empty stomach. The thinking goes that you're body is glycogen depleted then due to not having eaten anything all night. With no glycogen reserves to draw from for energy, your body has to burn fat to fuel itself. My fear here is that your body will also burn muscle as well. To counter that I usually down a protein shake before hand. Protein doesn't convert to glycogen as quickly as carbs do, and the extra amino acids may help spare your muscle during your cardio (IMO).
Other people swear by a HIT style of cardio training though. I'm not as well versed with this style, but I know there are probably a few dozen people on this board that can tell you all about it. I'm pretty sure it has to do with switching back and forth from higher and lower intensity intervals. Sort of a "go faster to burn more calories, but as you're heart rate rises, slow it back down for a while" sort of thing. I'm sure someone else can give you a more informed opinion on it.
Whatever you decide to run with, good luck brother!