A detailed explaination can be found here:

What is the process for applying Family Visa?

Conditions for applying Family Visa:

Work Visa Status should not be Labour
Salary should be 10,000 QAR or more and should be transfered in bank account.
Tenancy Contract should be done - The process for Tenancy Contract is explained here
Fill the Entry Visa Form also available in MOI Website

Attache the following documents, while applying for Visa:

Salary Letter from Employer (Arabic - Typed and addressed to MOI-Immigration Dept)
Copy of Your passport and Work VISA Page.
Copy of Attested Educational Certificates of the most highest degree
Attach other Educational Certificates, recommended
Wife's Passport Copy
Copy of Marriage Certificate Attested from Chamber of Commerce
Child(s) Birth Certificate(s) Attested from Chamber of Commerce
Copy of Electricity Bill in your name
Six Months Bank Statement, signed by the bank with evidence of proper salary transfer.
The documents should be submited to Ministry of Labour.

If any of the above certificates are not in English, you have to translate them in English and attested.

A must requirement is you should have salary of 10,000QAR or more and should be transfered to your bank account every month.