At a pull-up station, create a "step" of some sort that allows you to readily get to the top of a pull-up. This can consist of either a bench or plyo box placed beneath a pull-up bar. Or, if the pull-up bar is part of a power rack, place a barbell on a rack around a quarter or a third of the way up the power rack and use that as your step. Use that to step yourself up to the top of the pull-up range of motion - chin over the bar, elbows bent, using a wide overhand grip. From that position, lower yourself through the negative portion of a pull-up rep as slowly as possible, resisting the pull of gravity for as long as you can. Step yourself back up to the top of the pull-up range of motion and repeat. Do as many negative reps in this fashion as the set calls for, which will typically be somewhere around 3-5 negatives. The objective here is to build enough strength via negative reps that you're able to perform significantly more regular pull-up reps in a matter of weeks or a few months.
