diet, cardio, and weights. make sure you're doing squats and try to keep them in the 6 - 10 range. any higher and you're going more cardio when what you want is to
build muscle. the "lean/ripped" bit is the diet and cardio.
wait a minute: did you mean "thinner" thighs or "thunder" thighs?
if it's "thunder" thighs you're worried about, that's fat - get rid of teh fat and your thighs'll lean out. unless you're genetically gifted, you're not going to break out in ahnold-itis. if you want thick, muscular thighs, you gotta WORK for them.