The following 4 things are obligatory in tayammum performed instead of Ghusl or Wudhu:
• Intention (Niyyat)
• Striking or keeping both the palms on the object on which tayammum is valid. As an obligatory precaution, this should be done by both the palms together.
• Wiping or stroking the entire forehead with the palms of both the hands, and, as an obligatory precaution, its two ends commencing from the spot where the hair of one's head grow down to the eyebrows and above the nose. And it is recommended that the palms pass over the eyebrows as well.
• To pass the left palm over the whole back of the right hand and thereafter, to pass the right palm over the whole back of the left hand.