Originally Posted by viru§™
Lat pulldown doesn't have much carry-over to pullups at all. The best way to improve pullups is to do them.
If you can't do a single one then negatives is by far the best way. You can also use resistance bands wrapped over the bar and placed under your foot or knee depending on the size of the band.
Years ago when I couldn't do more than a few pull-ups, what I did was pulldowns with the knee-pad raise too high actually be in contact with my knee. I'll be the first to say, this wasn't the only reason why I improved, but very quickly I was able to do more and more.