Starfleet Rank List

These are the ranks as listed by Memory Alpha. Keep in mind that the ranks are in descending order (meaning the higher ranks are at the top, lower at the bottom), and when creating your character, also remember that the longer you have been in Starfleet, the higher your rank will be. Those just out of the Academy will probably not be Commanders or Captains (excluding the very rare exceptions, like James Kirk).

Flag Officers
Fleet Admiral (Fadm.)
Admiral (Adm.)
Vice Admiral (Vadm.)
Rear Admiral (Radm.)
Commodore (Cdore.)

Commissioned Officers
Fleet Captain (Fcapt.)
Captain (Capt.)
Commander (Cmdr.)
Lieutenant Commander (Lt. Cmdr.)
Lieutenant (Lt.)
Lieutenant Junior Grade (Lt. J.G.)
Ensign (Ens.)

Officer Candidates
Midshipman First Class (Mid1C)
Midshipman (Mid.)
Cadet (Cdt.)

Enlisted Ranks
Master Chief Petty Officer (MCPO)
Senior Chief Petty Officer (SCPO)
Chief Petty Officer (CPO)
Petty Officer First Class (PO1)
Petty Officer Second Class (PO2)
Petty Officer Third Class (PO3)
Crewman First Class (CRM1)
Crewman Second Class (CRM2)
Crewman Third Class (CRM3)