I strongly recommend using an app like Coach's Eye. You really want the ability to easily film and then review your lifts frame by frame. If you can do that, you don't need a great eye in real time. You'll be able to take your time, go through yoru checklist, and figure out what technique errors you're making. 

From a side view, look at:

1. the bar path (look at the end of the bar, it should be straight. If it's not, what's causing that?)
    
2. the torso angle (it should remain vertical)
    
3. the feet (do the heels stay down in the dip, and are the feet in the right place in the catch?)
    
4. whether not not the knees fully extended

From a front view, look at:

1. the bar (does stay in firm contact with the shoulders, or lose contact or shift down off the shoulders?)
    
2. the knees (do they fully extend and do they collapse inward?)
    
3. the feet (are the feet in the right place in the start and catch positions?)