After bleaching session, you should observe the following: 
1- Avoid any food/drink that causes colouring for a week ( example: coffee, pepsi, ketchup, sauces, etc ). Even toothpaste should be plain white
2- When you get the result, the Doctor's role ends and your task begins to maintain it
3- Clean the teeth properly and after each meal
4- Wash teeth well after drinking any juice or drinks that contains coffee or cocoa or pomegranate
5- Smoking or sheesha diminishes the result faster
 As the white thoub is easy to get stained, same is the case with the whitened teeth unless they be taken care of  .
And please note the following points
1- Whitening is not a coating or a layer placed on the teeth
2- No Grinding or rubbing or depigmentation but just changing the colour of the cleaned teeth