Eye the Prize
One of my bad tendencies is allowing my hips and shoulders to get open at address. I see a lot of amateurs do this, too. This is a critical mistake, since your body will always swing in the direction it's pointed, not in the direction you think it's pointed or where you've aimed the clubface.
I use alignment sticks all the time when I practice, and I have my caddie, Joe Skavron, check my body aim when we're at the range. If I know I'm aimed correctly, I can start the club back with confidence.