The lat pulldown has become more popular around gyms than the pull-ups. The reason is simple, pull-ups are freaking hard and most people cant do them well or just cant do them at all. Here are some ways to change that.
1) Lose excess weight/body fat-You need to be strong and lean to do pull-ups. The heavier you are the harder its going to be to excute obviously.
2) Do not train to failure-When your doing pull-ups if you always train to failure you end up with horrible sloppy reps and you just dont gain a benefit from it. In fact going to failure on pull-ups often tends to lead to decreases in strength and mass gains for reasons unknown, it just happens.
3) Elbows towards your sides-Think about driving your elbows down and back to really bring the lats into play and therefore avoid relying mostly on your biceps.'
4) Improve your grip strength- the stronger your grip the better your pull-ups will be. You can build grip strength by doing more deadlifts and reverse curls or by using fatter barbells. You can also do wrist curls and other exercises geared towards grip strength.
5) Train with different ranges-To do a bunch of pull-ups you need both strength and endurance. Make sure you lift with low rep ranges for strength and high rep ranges for endurance. You can use bands as assistance for the pullups if need be.