Basic ranking system for the Navy/Marines in
Babylon 5's EarthForce as follows*:

STAFF/FLAG OFFICERS
General (Joint Chiefs of Staff)
General
Lieutenant General
Major General

COMMISSIONED OFFICERS
Colonel
Captain
Commander
Lieutenant Commander
Major
Lieutenant

JUNIOR AND NON-COMMISSIONED OFFICERS
Lieutenant (Junior Grade)
Ensign
Chief Warrant Officer
Warrant Officer (Class 1)
Warrant Officer (Class 2)
Sergeant Major
Master Sergeant
Gunnery Sergeant
Staff Sergeant
Chief Petty Officer
Petty Officer First Class
Petty Officer Second Class

ENLISTED
Private First Class/Technician First Class
Private/Technician

*this assumes same ranks for both, assuming
that the Marines Corps or "GROPOS" comes under
the umbrella of the Space Navy

The following chain-of-command is applicable to
all parts of the armed services and off-world security in
the Earth Alliance,presumably including EA Intelligence
(ranks not given) and Psi-Corps:
Colonel
Captain
Commander
Chief Warrant Officer
Lieutenant Commander
Warrant Officer (Class 1)
Major
Warrant Officer (Class 2)
Lieutenant (and equivalent ranks)

Junior Officers are classed with the non-commissioned
officers to coincide with the NCO uniforms worn by
roughly half of B5's Starfury pilots.

Pilots usually go through three years training at Air Dome
without usually attending Officer Training school.
A similar process probably applies to officers, like
Major Kemmer in Earth Force security, i.e a
"Security Academy".

Sheridan and Lochley probably both attended Air Dome
after completing Infantry Training (although Sheridan
also attests to requiring passing an entrance exam
to the Academy) and then spent a fourth year at
Officer Training school.

Air Dome is described as accepting candidates
from aged 16, presumably an entrance requirement
would require some mastery of College-level
Physics.

Ivanova trained as a pilot after attending
university, it is probable she recieved
her Commission as Ensign because of this.
Similarly, Franklin would have attended
(and entered) the Officer Training school
on the basis of his medical qualifications.

I'm assuming the ranks for Earth Force security
are as follows while ranks for station security
would appear to fall under the senior enlisted
ranks.

There are at least five security levels, so
presumably the lowest rank is Level 1.

SECURITY OFFICERS
Major
Sector Captain [level 4?]
Sergeant
First Lieutenant
Second Lieutenant [level 1?]
[Security Cadet?]

[STATION SECURITY:
Warrant Officer
Sergeant Major (level 4?)
Master Sergeant
Gunnery Sergeant
Staff Sergeant (level 1?)]

The order for Security Officers is based on Laurel Takashima's
position on Mars as a Sector Captain
[Pilot episode: The Gathering]
and the abbreviated list of Psi Corps ranks and
officers
[Season 2: Spider in the Web]
Colonel
Commander
Lieutenant Commander
Sergeant
Lieutenant

Finally, a list of ranks for Starfury Pilots
based on estimations, patch insignia and
show dialogue (I am assuming that the rank
of Wing Commander is equivalent to the rank
of Major while assuming four ranks below
this to maintain consistency with the ranks
for Security Officers i.e lowest rank is
equivalent to Officer Training School Cadet):

PILOTS
Wing Commander
Lieutenant
Squadron Leader
Pilot Officer
Junior Pilot
Air Dome Cadet

Overview of equivalent ranks:
Lieutenant=Same rank Navy=
Sector Captain (Security),
Squadron Leader = Sergeant Major
=Lieutenant (Junior Grade) = Sergeant,
Pilot Officer = Master Sergeant=
Ensign = First Lieutenant,
Junior Pilot = Gunnery Sergeant=
OTS Cadet = Second Lieutenant

By the way....no Corporals are ever explicitly
mentioned, only NCOs. Based on the insignia
of the Sergeant Major in the episode GROPOS
(four chevrons top, three bottom surrounding
a lopsided star motif) and the lack of any
insignia for the Enlisted personnel I've
assumed the existence of seven non-commissioned
ranks, plus three Warrant Officer positions.
A Chief other than Garibaldi (CWO) is mentioned
briefly in Season 5 (I think) so I would assume
this refers to a Chief Petty Officer, fitting
in with Naval terminology.