Some simple changes to your squat could make a big difference, so I thought I'd stick a few of them together for anybody that wants to improve the squat. Ive taken some information from some other lifters and my own experience.
BAR PLACEMENT
The bar should go in a groove that is created when you hold your arms back between the posterior and medial head of your deltoids and right below the bulk of your upper traps. Its a little bit of a stretch for some people with bigger frames so a wider grip could be better with the elbows high, I grip the bar fairly close but wear elbow supports as I sometimes suffer being in this tight. If you have a medium to small frame you can try Keeping your head up and your elbows as far back as you can and down, the bar should stay put. With a closer hand spacing you stay tighter and in better control of the bar. Try and keep upright with your abdominals flexed. I squeeze my abs hard against my belt at the start of the lift and find it easyer to unrack the weight this way.
If your used to having the bar high on your traps, trying to squat with the bar low on your back, this will feel strange at first but with time gets easyer. Your balance will be affected having the bar in this area above the traps. I used to squat with a high bar placement and I used to get a lump at the botttom of my neck from where the bar was rubbing. I had to start from scratch to improve my bar placement, I just stuck with 60 kg's on the bar for weeks until I got it right.
FOOT POSITION
When I set up for the squat I position my feet pointing out, I find I get a lot more from my hip's and glutes. Try and position your feet at a ten to two angle. I find hitting seated calves heavy once a week helps your stability on the squat, I dropped this exercise for a few weeks last year and my foot position was all to cock.
CLOTHING
Try to wear a top or t'shirt that will let the bar sit nice on your back, I've seen people wearing hoodies and lycra tops it just makes your squat more difficult. Use plenty of chalk on your back, so the bar wont keep moving around and is snug you will feel stronger. As for what to wear on your feet this topic is debatable, Ive used a boot with a heel but I find I lean forward a lot and my squat is hunched over. Inzer make a nice squat shoe (
http://www.inzernet.com/)with a heel if you prefer that style of squating, my training partner uses cat's and can get away with this type of squating. I like to use a flat footed shoe, Metal make a nice squat and deadlift shoe (
www.gometal.com) that grips the floor and give you lots of stability. This type of shoe stops me from leaning over in the squat.
KNEE WRAPS
Knee wraps can add 20-30kg's to your squat, the best on the market are Titan, Inzer and Metal. I have recently used the Metal triple black line and they are good if they are wrapped extremely tight. I lately have been using them for my lighter set's, for my heavyer sets I find the Inzer red and black iron wraps are the strongest. They could also save your knee's from years of abuse.
POWER BELT
I think a good powerbelt keeps your body upright when squating improving your technique. You could add a few kg's to the squat just by using a belt. Dont forget to add a few set's without a belt to keep your lumbar muscles nice and strong. If you find it a pain in the but tightening your belt you could try a levere/buckle belt that you can adjust to fit your size. Its a lot easyer to use and it just clips shut.