There are only four acts fardh in wuzoo:
1-To wash the entire face from the hair of the forehead to below the chin, and from one ear lobe to the other once.
2-To wash both the hands including the elbows once.
3-To do Masah of a quarter of the head once.
4-To wash both the feet including the ankles once.
If any of the above is left out or a hair's breadth place is left dry the wuzoo will not be valid.