These pull-up techniques will not only get you stronger, they'll also teach you how to do better quality, more effective pull-ups.
Relearn pull-ups with negative reps. If you can't do a single pull-up, it's common advice to start with negative-only pull-ups. Jump or climb up to the bar, then lower yourself slowly. That same approach can be used when relearning loaded pull-ups.
Say you've decided to strap an additional 45 pounds to your waist. There's nothing wrong with focusing on good form from the top down using a weighted pull-up. Just stop yourself from dropping like a ton of bricks under the added load.
Do paused reps if you're trying to build muscle. Using a dead-stop during bodyweight pull-ups shuts off the stretch reflex, kills momentum, and creates the perception of much more weight being lifted. Simply pausing at full extension (at the bottom) can be more than enough of a tempo change to elicit a huge response from your lats. It also increases time spent under tension, which can be great for hypertrophy, especially to muscles of the back.
Alternatively, for a challenge to your concentric rep (the pulling UP part), try pausing your reps at the top of each lift. This is a true testament to the contractile strength of your lats. It also helps you zero in on maintaining lat involvement for the whole rep. A one-second hold at the top of each bodyweight pull-up using good form can make a world of difference.