Warm up really good, progressivly heavier.
Don't go lower than 6 controlled reps.
Don't lockout on any movement untill u r ready to rack the weight.
Look at your range of motion, make sure u aren't extending too far on the negative.
Make sure u r taking in 2-3g of esterfied creatine, or 10g (spread out) of mono. Also take 10-20g of glutamine spread out daily.(add it to every shake, and your first beverage in the morning)
Stick with the other joint supps u r taking.