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.
If you don't have access to a resistance band, just put a bench or chair behind you and rest one foot on there, use it for some minimal assistance to help you get up to the bar.