Definitely take the suggestions here but also consider a superset:
Because many people's biceps take over any lat-pull down movement it can be hard to visualize pulling from the elbows. Or, if you can "see" the process, it can still be hard to feel it. So, take a page from Christian Thibaudeau's play book and perform a superset as follows:
1st) a lat movement that does NOT involve the arm flexing--ie: no biceps. Something like a straight arm cable pulldown, or machine pullover, or similar
2nd) immediately follow that with a "regular" lat movement while your lats are still pumped. Stick to the part of the motion you can feel the lats the most on.
Personally I always feel the lats the most in the 1st half of a pulldown (the stretched position to the halfway position). But to each their own.
Also worth consideration is the way you START the motion of a lat pulldown. First, set the seat low enough that you have to stand to reach the bar. In other words when you are completely relaxed and stretched out the bar is NOT hitting the machine top so you still have the weight in your hands. I have long arms so sometimes depending on the machine i have to sit on the floor.
Second, get as much of a stretch as possible before starting to contract. Literally try to elongate your torso while holding onto the bar with straps. Third, when you start the motion, MOVE YOUR SHOULDER BLADES FIRST. Not your arms. Contract your shoulder blades down to start the motion. It is a little difficult to describe if you can't see it, but it definitely helps keep you from starting the pull with your arms, which most people--myself included--have been guilty from. I used this technique to break my habit.