How to Perform Tayammum
Question

How should a person do tayammum if he cannot find water or if he cannot use water?
Praise be to Allah.How to perform tayammum 
Al-Bukhari and Muslim narrated the hadeeth of ‘Ammar ibn Yasir describing tayammum . Al-Bukhari narrated it in a number of places in his Sahih. One of these reports (no. 347; 1/455 of Fath al-Bari) says: “ ‘It would have been sufficient for you to do this’ – then he struck the palms of his hands on the ground, then dusted them off, then wiped the back of each hand with the other, then he wiped his face with his hands.” 
Abu Dawud (317; 1/515 of ‘Awn al-Ma’bud) narrated it with the same isnad as al-Bukhari, apart from the Shaykh of al-Bukhari (Muhammad ibn Salam), instead of whom he mentioned Muhammad ibn Sulayman al-Anbari, of whom al-Hafiz said in al-Taqrib (2/167): he is saduq (truthful). This version of the report says: “He struck his hands on the ground and dusted them off, then he struck his right hand with his left hand, and his left hand with his right hand, then he wiped his face.” 
Al-Hafiz mentioned in al-Fath (1/457) that al-Ism’ili narrated it with the wording: “It would have been sufficient for you to strike your hands on the ground, then dust them off, then wipe your right hand over your left and your left hand over your right, then wipe your face.” 
What should be wiped first in tayammum?
Al-Shanqiti said in Adwa’ al-Bayan (2/43): 
“This hadith of al-Bukhari states that the hands should be wiped before the face.” 
Shaykh al-Islam said in al-Fatawa (21/423): 
“The report of al-Bukhari clearly shows that the back of the hand should be wiped before the face. The fact that in another report he said ‘the back of the hand’ indicates that he wiped the back of each with the palm of the other.” He also said (21/425:  “But the report which was narrated only by al-Bukhari shows that he wiped the backs of the hands before the face.” (See al-Fatawa, 21/422-427) 
Based on this, the way in which tayammum is done is to say Bismillah with the intention of doing tayammum , then strike the ground once with the palms of the hands, then wipe the back of the right hand with the palm of the left, and the back of the left hand with the palm of the right, then wipe the face with both hands. Then the same du'as that are recited after wudu’ should be recited after tayammum. 
And Allah knows best.