Think of lat pull-downs as the opposite of pull-ups in terms of movement. For this exercise, you'll need gym equipment or a home gym setup. Lat pull-downs, as the name suggests, work the latissimus dorsi.
Seat yourself at the pull-down machine, grab the bar the same way you did with pull-ups -- palms facing outward and arms slightly wider than your shoulders. With a slow and measured movement, pull the bar down to your chest and hold it there for a second or two. Slowly bring the bar back to its original position, allowing the upward tension to engage your muscles [source: Murphy].
Start with a weight you can reasonably handle for 10 repetitions. Complete three sets. Remember, form is important -- don't sacrifice form by using too much weight. You'll be able to increase the weight with time.