If you have exams first thing is to study hard. As Allah says in the Quran

€œI give humans according to their efforts 

After you have studied hard do the following Inshallah you will get great marks in your exams. This is a tried and tested wazifa. It works each time.

After every salah do a sajda and in the sajda read Surah fatiha once only. 

In the sajda when you come to €œiiya ka na budu va iiya ka nasta een€. Repeat it 21 times. then complete the Surah till the end and raise your head from the sajda. Then do a dua for your exam. You must do this after every salah. 

Darood/salavat 1 times before and after the dua is must.

This wazifa is very small and takes 2-3 minutes and is very powerful. Continue until your result comes out. 
Make sure you also read darood/salavat fadal from the website every friday too.