Before every daily obligatory prayers it is necessary for a person to do Wudhu (ablution).

Wudhu consists of two parts:
Sunnat (consists of):

Washing both hands from the wrists

Washing the mouth (Gargle)

Rinsing the nostrils

Wajib (consists of):

Niyyat (Intention):
Niyyat should be perfomed in ones mind as follows: "I perform the wudhu in order to cleanse myself from impurity and to make myself eligible for Namaaz, wajib qurbatan Ilallah.

Washing the face:-
The portion of the face to be washed is from the forehead (from the point where the hair starts growing), to the end of the chin in length and its width is as much of the face that comes between the thumb and the middle finger when they are spread (wide open).

Even if the small portion of the face is not washed, Wudhu will be void. As a precaution, one must wash a little bit beyond the required limit. Any dirt on the face (or hands) which may prevent water from reaching the skin must be removed before you start the wudhu.

The face and hands should be washed from above downwards, and if one washes the opposite way, his Wudhu will be void.

Washing the hands from the elbows to the tip of the fingers:-
After washing the face, one should first wash the right hand and then the left hand, from the elbows to the tips of the fingers. In order to ensure that each elbow has been washed thoroughly, one should include some portion above the elbow in washing. If before washing his face, a person has washed his hands up to the wrist, he should, while performing Wudhu, wash them up to the tips of the fingers, and if he washes them only up to the wrist, his Wudhu is void.

While performing Wudhu, it is obligatory to wash the face and the hands once, and it is recommended to wash them twice.

After washing both the hands, one performing Wudhu should wipe the front part of his head with the wetness which is in his hand, from the upper part, downwards.

The part on which wiping should be performed, is one fourth frontal part of the head. It is sufficient to wipe as much at any place in this part of the head, although the recommended precaution is that the length should be equal to one finger, and its breadth should be equal to three joined fingers.

It is not necessary that the wiping of the head should be performed on its skin. It is also in order if a man wipes the hair on the front of his head. However, if the hair are so long that when combed they fall on his face, or on other parts of his head, he should wipe his hand on the roots of his hair, or part the hair and wipe the skin. If a person collects his hair on the front side of his head, or on other parts of his head and wipes them, or if he wipes the hair of other places, such a wiping would be void.

After wiping the head, one should wipe with the moisture present in one's hands, one's feet from any toe of the foot up to the joint. As a recommended precaution, the right foot should be wiped with the right hand, and the left foot with the left hand.

Wiping of the feet can have any breadth, but it is better that the breadth of the wiping should be equal to three joined fingers, and it is still better that the wiping of the entire foot is done with the entire hand.

As a precaution, at the time of wiping the foot, one should place one's hand on the toes and then draw it to the joint, or that one should place the hand on the joint and draw it to the toes. One should not simply place the whole hand on the foot , and pull it a little.

While wiping one's hand and feet, it is necessary to move one's hand on them, and if the feet and head are moved leaving the hand stationary, Wudhu would be void. However, there is no harm if the head and feet move slightly, while the hand is be ing moved for wiping.

The parts of wiping should be dry, and if they are so wet that the wetness of the palm of the hand has no effect on them, the wiping will be void. However, there is no harm if the wetness on those part is so insignificant, that the moisture of th e palm overcomes it.

Most of the notes on this page are from:
http://www.al-islam.org/laws/wudhu.html