One of the most frustrating things about fitness is not making progress. Whether you're a weightlifter, power lifter, body builder, cyclist, runner or a CrossFit athlete, through and through, you will eventually plateau. In the early stages of whatever exercise modality you are loyal to, you experience massive improvements simply by doing said exercise consistently (see Coach Josh's blog "Three Tools for 2017" to see what this means for weightlifters). Eventually though, you will plateau. It's not a question of "if" you plateau, but "when." After you master a movement, take a snatch for example, you will have to do more than simply snatch to add a kilo to your personal best.
An essential element to voiding plateaus is accessory work. You will only be able to perform as well on a main lift as your body's weakest muscle group will allow you to perform. In a deadlift, if your low back isn't strong enough to be the barbell off the floor, you won't be setting a new personal record until you strengthen your lower back. In the bench press, if your triceps aren't strong enough to lock out the weight, again, you obviously won't be PR-ing your bench press until you strengthen your triceps.
Seems simple right? Well, it's not as easy as it sounds. Let's look at "Grace," a CrossFit benchmark workout. "Grace" is 30 clean & jerks for time and, if scaled appropriately, should be done somewhere in the range of four minutes or less. Let's say you can't seem to break the four minute barrier. Assume your movement pattern is good and technique isn't the issue. However, most of the time, you think that you need to get a little better at cleans to improve your time; or maybe you feel like we need to get better at the jerks. Right? In actuality, your clean and jerks probably aren't limiting you, the movement itself is not limiting you. I'd bet you a burrito bowl (double meat) that doing MORE clean and jerks wouldn't be very beneficial.
My initial guess would be that you need to improve your aerobic energy system which requires you to do steady state cardio at a very low intensity for a long duration of time. For that athlete, the accessory work that I would prescribe would be rowing and/or biking intervals for 30+ minutes a few times a week. Definitely NOT more clean and jerks.
What about a one rep max deadlift? Maybe you can rip 300 pounds off the floor like nothing but 315 buries you every time. Your limiting muscle group could be your lower back strength, upper back strength, lats, glutes, hamstrings or a combination (or all) of the above! But what about your grip strength? It's possible that if you spend some time doing some heavy farmer's carries, your deadlift will go through the roof. Think about that one. Simply walking with some heavy weight in your hands for a few weeks could increase your deadlift dramatically. The interesting thing is that you don't even have to deadlift.
Recently, I worked up to a max power snatch and bested my previous one rep max by twelve pounds. What did I do differently? I wasn't squatting, I wasn't doing heavy pulls, I wasn't even snatching...I was jumping! Using box jumps as one of my main accessory exercises (I used many different variations) made me faster off the floor and throughout the pull. My point is that if you want to make an improvement on a main lift, doing more of that lift probably isn't the ticket. You should be honestly assessing yourself, and identifying what your limiting factor is. After you identify what is limiting you, appropriately prescribing accessory work to bring up the weaker muscle group or limitation will shatter whatever plateau you have been experiencing.