Feet should be shoulder-width or slightly wider apart.
At the bottom of the rep, your elbows should be up high, such that they are in front of the barbell.
Use a wider grip if you cant lower the bar to your collar bone.
Take the bar and place behind your neck on the shoulders. Feet should be shoulder-width or slightly wider apart.The hands hold the bar just outside the shoulders and elbows should always be forward of the bar.
Dip down at the knees and use that momentum to drive the bar upwards. Bend your knees to a quarter squat and as you drive back upwards, press the bar up with your shoulders and arms. Make sure that when you bend down at the knees, you dont push your hips forward. You want to maintain that hip angle so that you can use the power that comes from extending (straightening) the knees and hips. Its a fast, snapping motion.
Finish with arms straight and the bar locked out overhead. At the same time, the hips come back slightly so that there is a slight curve in the lower back at the end. This helps to give the drive some extra oomph when the weight gets heavy.
Then bring it back down behind your neck and let it rest on your shoulders. Repeat.
Don't move the barbell around your head. Rather, move your head out of the way by retracting it and moving your torso back. The barbell should travel in a straight vertical line, up and down.
Don't let your chest come forward. People have a tendencies to lean forward with their torso when bending at the knees before executing the push press.