Squats belong to the exclusive club of compound movements that trigger growth you could never replicate by diddling around with isolation movements only. Don't get me wrong, there's a time and a place for isolation, but when you're looking to build a foundation of raw power and mass, compound movements are unbeatable.
So getting your repertoire of compound exercises in order is crucial, plain and simple. You want to be able to move as much weight as possible with the best form possible, which translates directly to substantial muscular development. Typically, you see young guys adhering more to the first part than the latter. However, unlike benching, squats aren't much of an "ego exercise", so there's usually hope.
Why do I talk about hope? Aside from the obvious risks of injury that comes with sloppy form, squats are actually an exercise that can make you STRONGER by NOT cheating. When people cheat on their squats, they usually aren't only gambling with their joints and spine, they might even be robbing their egos of the cheap thrill that comes with adding some more weight to the bar.
POINT #1: FORM
Check your form! Straight back, wide stance, abs tense, eyes towards the ceiling throughout. You should FEEL the balance in your body. Also make sure to bend your knees in sync with the tilt of the lower back. You're not doing good mornings with 300 lbs on your shoulders! If you feel unbalanced, hurt, or is otherwise unsure of the proper execution, don't hesitate to talk to a professional Personal Trainer.
You will probably get a little weaker at first, but take my word for it - if you're doing it right, you'll be back and beyond your previous weight within a couple of months!
POINT #2: CARDIOVASCULAR CAPACITY
Especially if you're doing high-rep sets, you might be familiar with the sensation of light-headedness and dancing black dots in front of your eyes somewhere around the 13th or 14th rep. You could get to this state faster if you held your breath - and you'd probably not be able to pull off more than 3 or 4 reps before it started getting really bad. The reason is pretty simple: You're running out of oxygen!
When squatting, you're engaging in extremely oxygen-consuming work. Your need oxygen to get energy to the muscles. Not so much for the energy itself, but to enable the whole process. It's not unlike a gasoline engine - you need the air for the internal combustion, even though it's mostly the gasoline providing the explosive energy. If you don't take in enough oxygen, you can't utilize enough energy, and you end up running on stored ATP and Creatine. These sources run low in a hurry when you're doing some serious lifting.
What we're left with after, say 8 to 10 reps or so, is highly dependent on how good your body is at taking in plenty of oxygen in a short amount of time. The more your body can take in, the more energy gets utilized, and the more reps you can squeeze out. Pretty simple, huh?
The key issue here is - of course - to prime your ability to absorb oxygen. Now for the bad news. The only way to do this is to spend some time pounding the concrete, biking, or anything else that gets your heart rate up and going. Make sure to get at least 3 rounds of cardio for 20 minutes or more per week, and keep that pulse higher than if you were out to just burn off the love handles.
POINT #3: STEALTH
This clever method is so simple that it tends to be all but forgotten in favor of other, more complex strategies. However, the stealth method is hard to beat when you're looking to pump up the weights in compounds movements like squats. The basic principle is this:
Your body doesn't really know the difference between 300 lbs and 305. Those puny 2.5's on each side are a thimble in the ocean. Odds are, you'll probably have no problems doing the same amount of reps with 5 lbs extra.
Then you sneak on another 5 lbs a week or two later, you've gotten used to 305, so that 310 doesn't really make much difference either, now does it? …And so it can go on for quite a while. In the span of a few months, you could actually have added 40-50 lbs to your total, while still doing the same amount of reps!
Granted, the pace might not be quite as exciting as heavy negative training, but you can be fairly sure to get the weights up, slowly but steadily, without running undue risk of injury. The only real downside is that you have to ditch the periodization-strategy for legs while doing this.
The conclusion - of course - is to periodize stealth training with normal high/low-rep alternating periodization! As in doing 3 months of stealth training, then do 6 months of "normal" periodization (4-6 week cycles of lighter vs. heavier training - read my last article all about PERIODIZATION here!), and then go back to 3 more months of stealth training. You'll probably notice a slight setback in strength when taking up the stealth again, but it'll rebound quickly.