There are fundamentals and basics of playing the saxophone that every student--and instructor--should know. It is imperative that good habits in the areas of good posture, and good embouchure be set and practiced from the beginning. It will take far less time to create good habits than to unlearn bad posture or a bad embouchure.
There may some saxophone fundamentals and tips I offer about posture others, alto players in particular, might disagree with. My thoughts on embouchure may cause clarinetists to raise an eyebrow. But remember, saxophone is a different enough instrument to set it apart from its other woodwind cousins.
Posture, especially when sitting, is critical to enabling good breathing or making it more difficult.
Playing sax while standing seems more natural than sitting. The only factors that need to be in place are the music stand, and balance. The music stand should be raised so the players face is looking straight and not down. Balance is achieved by the placement of the feet. They should be shoulder width apart, and perhaps the right foot slightly behind. Try not favoring one hip over the other. This will lead to fatigue and soreness.
Embouchure is an issue that is more personal, due to the uniqueness of every player's teeth, oral cavity, tongue, and throat. What's important is that the player forms an open, shaped, channel for the airstream to move from the lungs to the mouthpiece which is free from obstruction and large in volume.