There are ten prohibitions in performing an ablution
1-When relieving one or urinating in the toilet or outdoors, one should not turn one's front or back towards the Qibla. It is makruh also to stretch one's feet towards the Qibla or the Quran. If the Quran is above one it will not be makruh.
2-It is haram to open one's private parts near someone in order to make taharat.
3-One should not make taharat with one's right hand.
4-When there is no water, it is makruh to make taharat (to clean oneself ) with food products, manure,bones,animals food,coal,someone else's property,reeds,leaves. Instead of that should have "Tayammum".
5-One must not spit or throw mucus into the pool where one makes an ablution.
6-One should not wash one's limbs of ablution much more or less than the prescribed limit, nor wash them more or less than three times.
7-While washing the face, one must not splash the water on one's face, but pour it from the upper forehead downwards.
8-One must not blow on or over the surface of the water.
9-One must not close one's mouth and eyes tightly. If even a tiny part of the outward part of the lips or the eyelids is left dry, the ablution will not be acceptable.
10-One must not make masah on one's head, ears or neck more than once after moistening the hands each time. But it can be repeated with moistening the hands again.