This question answered several times in this site, please use the search box on right hand side (top) of this screen, you will get the proper and authentic answer,

in a nutshell:

Your salary should be more than 10000 QAR
6 months bank statement ( though not mandatory)
Attested education certificate.
Marriage certificate attested.
Kids birth certificate attested.
contract.
Water & electricity bill in your name ( not mandatory)
one more thing - Luck.