Yep, what
JustinDetail said
Especially his advice about making health/exercise/etc. a lifestyle. You don't have to become a weirdo about it, just not missing workouts will make a huge difference. Long-winded answer follows:
Gotta understand how to exercise to get the right results. To do that you really need to study the subject. You make muscles grow by overloading them so they compensate by growing bigger and stronger. Read books like The Poliquin Principles to learn how your muscles work and how to exercise them properly. Use freeweights instead of machines and remember that gravity pulls straight down. Again, learn what your muscles do and how to exercise them.
Don't worry about leg work making your legs too big. It simply won't be a problem (heh heh, nobody's gonna say "gee, your legs are too muscular"
). Hard leg work is the #1 type of weight work for most *any* desired outcome. As the saying goes, "if you want big arms, work your legs"; it's true.
Do brief but intense cardio on an empty stomach, first thing in the morning. It *will* decrease your bodyfat if you eat right (so you're not just putting fat back on). But it'll happen slowly and gradually and you have to stick with it. This will also offer great cardiovascular benefits. Working hard for 20-some minutes will do more for you than doing easy cardio for an hour the way a lot of people do it.
Don't eat/drink empty calories. Make that a lifelong daily regimen; yeah, you *will* east/drink 'em some time if your a normal human being, but it shouldn't be something you do regularly. Eat small, balanced, meals throughout the day, I shoot for maybe every three hours.
Remember that it took a while to get fat so it'll take a while to get lean. Think long-term
Get a body-composition test done and find out how much fat you're really carrying. Then get it done again at regular intervals so you can objectively track your progress. It's not expensive and most sports rehabilitation/etc. type facilities can do it.