Don't want to clog the thread about my terrible form but I just recorded this in my basement trying to see if I'm following what you guys are saying. I think I see some improvement, especially in the last few reps.
https://www.youtube.com/watch?v=pB00RbXA8-E
All help is appreciated.
I wouldn't practice on anything less than135 so you can really get the appropriate starting height down.
Also, if you're really pulling the slack out like the video Brolic posted, that light weight should be hovering before you pull. For me, the weight hovers up to around 165. I'm sure for guys like Brolic it hovers at 225+
I used to run into very similar problems as you.
Sitting back into the start position, pulling the slack with my legs and humping the bar all helped.
Another good cue is nipples towards the wall (to get your chest up)
This was from a little while ago, and I'm nowhere near brolics level, but it gives you an idea
http://instagram.com/p/mFsaoBI6W4/