If you are trying to get stronger dont focus on form the last couple sets. Get the weight up and down the next time a little more form on the higher weight and see if you can go up again. Push yourself harder than whats comfortable. Have a spotter if coarse, if you aren't struggling (allot) then you aren't trying hard enough!
Not only asking for injury, but ingraining poor motor programming - escpecially in someone who has limited experience performing a movement.
It goes along with the saying perfect practice makes perfect.
You guys are right. That is for more experienced lifters. And yes some exercises it would have a negative effect. No argument with that. An injury is the most annoying thing possible when lifting. Be careful, stay classy!