1 - To wash the entire mouth very well. Drinking a mouthful of water will do, yet some (savants) said that it would be makruh .
2 - To wash the nostrils. A ghusl will not be accepted if one does not wash under any dried mucus in the nostrils or under any chewed pieces of bread in the mouth. According to the Hanbali Madhhab madmada (rinsing mouth) and istinshaq (washing nostrils) are fard  both in ablution and in ghusl.
3 - To wash every part of the body. It is fard to wash every spot on the body if there is no haraj (difficulty) in wetting it.
 makruh: (act, thing) improper, disliked and abstained by the Prophet (‘alaihi ‘s-salam); makruh tahrima: prohibited with much stress.
 fard: an act or thing that is commanded by Allahu ta’ala in the Qur’an al-kerim. Fard (or fard) means (any behaviour or thought or belief which is) obligatory. Islam’s open commandments are called fard (pl. faraid).