Do these or t-bar or as plain bent over rows. Currently I am tring to build my lower lats so I use the close grip pulled in down low. Remember when doing this exercise to stretch out at the bottom and to pull back with the elbows then the shoulder blades at the top.
Allow the bar to pull you out to full extension at the top of the movement. Pull down in a controlled manner - do NOT sway your body to add momentum. The wide grip tends to help build width in the upper lats.
Pull through the movement with your elbows here, the whole time keeping your back arched. This exercise gets your entire lat, personally I find it good for my lower lats in particular though.
The Results
Put the seat back 30-40 degrees learn back into it through-out the movement. Do one arm at a time, it helps concentration. At the bottom of the movement let the arm hang, this will make it harder but will give a you a more complete development at the end of the day. As an alternative rest your triceps against the sides of the bench as you bring the weights up at a 90 degree to the bench (see photo), do both arms together though for balance.
Seated or standing. Hold hands vertical to floor. Do not swing or jerk body at all. These will also help build your forearms.
Get a weight you can do 15 reps with. Do a set of 10, rest 10-15 seconds, do another set of 10, rest, do as many as you can (limit 10), rest, etc. Until you can only do 3 reps. Put the weight down - feel the burn. Maybe do a second set. Try using wide or very narrow grips for these to hit different parts of the arm from your normal 'work' sets.