A US Citizen (USC) may petition for his/her immediate relatives and other family members for immigrant visas.  Only immediate relatives of USC's can qualify for family-based immigrant visas immediately, with no wait time.  The other, more distant relatives must wait for visa availability as the information is published by the Department of State, in its Visa Bulletin, every month. 

Immediate Relatives are defined as:

• ​Spouses of U.S. citizens
• Children (unmarried and under 21) of U.S. citizens; or
• Parents of U.S. citizens (The petitioning citizen must be 21 or older.)

Visa Bulletin

Other Relatives must track the visa bulletin to determine when their priority dates are current before the USC can petition for them.  If your relative does not fall under the definition of an Immediate Relative, you should determine (1) the beneficiary's relationship to you and refer to the appropriate preference category on the visa bulletin, (2) the beneficiary's foreign state of chargeability, and (3) whether the beneficiary's priority date is current by looking at the most updated version of the visa bulletin. When the beneficiary's date is current is when you would be able to file for an immigrant visa and adjust his/her status to a Legal Permanent Resident.  

• ​ Ensure that you meet all the requirements to petition for your immediate relative or other relatives
  
• Ensure that your petition is filed the month that they are current, to avoid the adverse effect of the possibility of retrogression (retrogression can happen any time, read about it  here )
• File Form I-130, Petition for an Alien Relative 
  
• File Form I-485, Application to Register Permanent Residence or Adjust Status 
  
• File Form I-864, Affidavit of Support 
  
• File any waivers of inadmissibility, if required and eligible 
  
• ​Ensure that all forms are filed correctly with the correct fees, sending in separate checks if required by the USCIS.