In a recent article on T-Nation (not work/family safe), Jim Wendler was asked:
"[...]what are the best lifts to bring up the squat?
JW: I knew when I addressed the deadlift last month that this question was coming, so I've prepared accordingly.
You have to squat. And do lots of squats.
Are you squatting? [Explicative Deleted] you if you lied to me in the first question.
See you next month!
He doesn't stop right there, though. He goes on to list some useful assistance exercises for the back squat. But he's got it right on the nose in his initial advice.
What's the best lift to improve your back squat? Do back squats. Clean up your technique and squat more.
Best lift to improve your deadlift? Do deadlifts. Clean up your technique and deadlift more.
Best way to improve your sprinting? Do sprints. Clean up your sprinting technique and sprint more.
Best way to improve your punching? Punch. Clean up your . . . okay, you see where this is going.
It's a good reminder we all need about keeping it simple. Assistance exercises, accessory work, strength and conditioning for sports, whatever - it's all meant to round out your training. The majority of the time, what will improve your basic lifts and basic sports skills is working on them directly. If you're trying to land more left hooks, work on the setup and execution of your hook. If you're trying to bench more, get right in to working on the bench. Don't spend hours trying to find the one tiny little extra that will solve your problems. Practicing the basics will solve them.
Work on the core of your sport, your lifts, your training. Keep it simple. The assistance work will help, and it is important. Just not as important as the main, core lifts. Or your main, core, training.