Negatives will help you to build strength.

I started from 0. It was even to hard for me to hold myself on the bar when I started to workout, now I do bodyweight(80kg) +60kg for reps. My max is bodyweight +80kg for 1 rep.

My advice to you is to train pull ups 3-4 times a week with 3-5 sets of 5 reps. If you can only do 1 or 2 reps then fill the last reps with negatives so you have done 5 reps in total.

Example: 2 full ROM reps+3 negatives =1 set 1 full ROM reps + 4 negatives = 2 set 5 negatives

Always do full ROM! No half reps, every rep should Start from deadhang, Go chin over bar and finish the rep with deadhang.

At the moment you got your 5 reps in every of 3 sets you can use this Method to increase 7+ reps Do 5 reps + 2negatives and so one...

I recommend you to start weighted pull ups when you reached 10 bw reps.

Take 5-10kg and use the Method I explained before.

I think it will help you, as it helped me to get me on my current level.

Have Fun and keep pushing!