Take a deep breath and begin singing a note. Instead of pushing the note from your diaphragm, push the note out through your throat. As the note begins to rise in pitch, concentrate on working your vocal cords to lift the note you're singing. The outer edges of your vocal cords vibrate when you sing falsetto, so close your eyes and visualize the note rising. This will cause your vocal cords to shift naturally, raising the pitch of your falsetto. Hold the note as long as you can, always controlling the amount of air you let out behind it. The air flow should be gradual. Too much air coming out at once will force the falsetto to lower.
Place a hand on your chest. If you feel your chest vibrating, you are not singing falsetto. When you sing from your diaphragm, your chest will vibrate. This is the proper way to sing in your natural voice, but completely opposite of what you need for falsetto. Stop, take a deep breath, and move your voice to your throat.
Scales are a good way to work on getting strength in your falsetto. Since falsetto is the softest form of the human voice, you will never be able to achieve the power you have when you sing from your diaphragm. You can strengthen your falsetto to extend the dynamic tone and range and to prevent yourself from squeaking. Sing scales on a regular basis, using your falsetto voice. Focus on varying the rhythmic presentation of each note. Hold some out longer than others and do them ascending and descending. As you sing your scales, concentrate on breath control. This more than anything else will help you get the most out of your falsetto.