Turn on your tuner and place it as close to the saxophone as possible. Place the tuner near the bell to get an accurate sound. Play the G that sits on the second line of the staff. If the tuner shows that you are sharp, pull out on your mouthpiece and try the pitch again. If the note is flat, push in on the mouthpiece to raise the pitch.
Warm up on the alto sax by playing long tones. Play whole notes by starting on C in the middle of the staff and descending a half step to B. Ascend back to C and move down a whole step to B-flat. Continue this series by adding a half step each time until you hit G on the second line of the staff.
Play the following series of notes on your saxophone while the tuner is on: D, E, F-sharp and G. Hold the G out and see if the saxophone is in tune. If the needle, or digital readout, of the tuner is not directly in the center, adjust the mouthpiece by pulling in or out until the instrument is in tune.