Check your smoke alarm for a "hush" or "silence" button. The hush button will only silence the alarm for approximately 10 minutes before the alarm starts up again, unless the source of smoke is removed in that time period.
Wave a towel near the alarm to silence an alarm that doesn't have a silencing button. This will cease the alarm only temporarily.
Open doors and windows to ventilate the room with the smoke alarm. Fresh air will filter out the smoke that's causing your alarm to go off.
Call your local fire department for instructions on what to do if your smoke alarm continues to go off even after the room has been ventilated.