Hi Karina!
Well, muscles are naturally lean, but we women often have a layer of fat covering all our muscles. When that is the case, continuing to work our muscles once a week (each) will preserve the muscle tissue while doing a variety of cardio activities 3-6 times a week will help shed that fat.
Eating sensibly (knowing what we are eating, a food diary is *very helpful* is also extremely effective.
Finally, the most important ingredient to this recipe is time and patience. One of the things that marks a seasoned exerciser- a lifelong exerciser- is the ability to see ahead, and the courage to modify exercises and work up to them slowly over time.
With these three components your body will get lean.
A side note- some muscles are leaner (like meat at the grocery store-- less marbelized) than others. Ours get that way too, after years of exercising, they get dense, and strong, and compact.