Step 1: The Right Ticker.
This trick will not work with DC POWERED clocks. (i.e. atomic clocks, watches, potato clocks, etc.)
DC powered clocks use batteries only.
Step 2: The Face!
1) RELAX your face, slightly close your jaw, and blow. It should sound like a gust of wind.
2) While blowing, FORCE your lips together. The result will sound like a cross between a machine gun and a fart.
If you're struggling, search "How to Blow Into a Trumpet Mouthpiece"www.google.com/search . It should help.
If you still have problems, wash your face with warm water. this will help relax.
If you STILL can't do this, then buy one of these things. www.amazon.com/Snoopys-Harp-Snoopy-Jaw/dp/B0002I90XS
If you don't want one, then read the comments below, the community seems to have really good alternate ideas.
Step 3: Gaze at Clock
I hope this works for you, and feel free to ask any questions!
...and don't forget to rate!