Check the placement of your reed. If your mouthpiece has a large tip opening, then place the reed higher than you would with a normal tip opening. The reed should align almost evenly with the top of the mouthpiece. With a larger opening, the reed would rest slightly past the edge.
Check the reed you are using. You may not have moistened the reed properly before you began playing. You need to moisten the reed for at least two minutes in your mouth before securing it on the mouthpiece. In addition, check the thickness of the reed you are using. For example, you should not play a classical reed with a jazz mouthpiece, as it can be too hard for the embrasure.
Adjust your embrasure. Oftentimes an airy tone is the result of a loose embrasure. Tighten the corner of your mouth on the mouthpiece and strengthen the muscles around your mouth.
Make sure there are no cracks or chips in your reed. This will affect your tone.