If you are having trouble getting the bar over your head:
-Before you unrack the bar, be sure to pull your elbows down into your sides with your lats. This will keep your upper back tight and give you a solid platform to push off of.
-After you are positioned under the bar, take a deep breath and hold, squeeze the bar as hard as possible, and unrack.
-After the bar is unracked, take a step back, let some air out, take another deep breath and hold. Now you’re ready to press.
-As you begin to press, arch your upper back to get your head out of the way so you can push the bar straight up. If you push it in front of your face and away from your body (in the sagittal plane), you’re fucked.
-As soon as the bar passes your face, drive your head under the bar and continue to push the bar up in a straight line. Breathe out once you are sure you will lock the weight out.
-In the finished position, the bar should be over the back of your head.
-To begin the next rep, take a deep breath and hold. This breath should be held for the duration of rep #2 (until you pass the sticking point).
-When lowering the bar, just reverse the process of pressing it while actively using the lats to pull the arms down. You should, in my opinion, lower the bar to the base of your neck or at least below your chin. This enables you to get maximum tension into the lats and triceps before pressing (or at least that’s how it feels).
-I have also found that it helps the lower back significantly if you actively contract the glutes throughout the set.
-Also, if you aren’t already doing it, wear a belt and use a false grip. The belt helps with trunk stability (duh) and the false grip just helps you “feel” the bar path better than a thumbs-around grip. I also use wrist wraps (because they can take a beating with several heavy sets of pressing per week) and elbow sleeves (because they are just about always sore from something).
Hope this is helpful. The video is me trying to do my best approximation of what I’m describing above.