I would say my bench was pretty bad. I just recently "perfected" it. I think the biggest issue was the idea that you have to flare your arms out 90 degrees to focus on the chest. Also, my back was flat and my feet weren't firmly planted.
Having corrected this I can feel the difference when I bench.
Also my overhead press. I think most people think you have to take a wide grip in order to "focus" on the shoulders. Well, like most people I did this with a grip that was wider than necessary, inefficient, and hazardous to the shoulders.