Your first breath
When you take your first breath you want to fill up your lungs as much as you can. Breath from your stomach and not normally. It's ok if your shoulders move a bit but try no to move them much.
Very First Note
when you take and make your first note make sure you use warm air and not cold air. So when playing think of fogging up a cold window and not simply trying to blow air. Aswell you don't want to puff your cheeks out. Although it isn't that bad if you do it can become a really bad habit and the muscles in your cheeks help with the compression of air. So if you're having trouble playing a note in the first place then try keeping your cheeks in.
Your Core
Another part of your body that helps with the compression of your air is your core. Make sure when you play you always squeeze your core in order to compress your air and that helps with getting different air speeds and different air speeds help you get higher or lower notes.