FLC OF A B737-400 TAXIED WITHOUT CLRNC AFTER LNDG RESULTING IN TWR LCL CTLR INTERVENING TO ADVISE THEM TO CONTACT GND CTL FOR TAXI CLRNC TO THE GATE. THE FO HAD CONTACTED RAMP CTL FOR GATE INFO AND FORGOT TO CONTACT GND CTL FOR TAXI CLRNC. CAPT ASSUMED THAT THE FO HAD RECEIVED TAXI CLRNC.

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WE LANDED ON RWY 24R AT LAX AND HELD SHORT OF RWY 24L AT THE TXWY Z HIGH SPD TURNOFF. WE WERE THEN CLRED TO CROSS RWY 24L AND HANDED OVER TO GND CTL ON THE ARPT N COMPLEX. WHILE EXITING RWY 24L AT TXWY Z; I CALLED UP RAMP TWR ON RADIO #2 TO ASCERTAIN WHETHER IT WAS CLR FOR US TO TAXI INTO OUR ASSIGNED GATE. RAMP TWR ASSURED US THAT BOTH THE GATE AND THE XX ALLEYWAY WERE OPEN FOR US TO COME ON THROUGH. I TURNED AND TOLD THE CAPT THAT BOTH THE 'GATE AND THE ALLEYWAY ARE OPEN;' AND IN SO DOING; DUPED THE 2 OF US INTO SOMEHOW THINKING THAT WE WERE CLRED TO THE GATE. AFTER TAXIING FOR A WHILE ON TXWY E TOWARDS OUR GATE; TWR CAME BACK TO US ON RADIO #1 AND TOLD US TO CONTACT GND. NOW REALIZING OUR MISTAKE; I DID SO; SAID I WAS SORRY AND ASKED PERMISSION TO CONTINUE. WE WERE NOW CLRED TO OUR GATE. IN MY MIND; THIS INFRACTION AROSE BECAUSE I BROKE THE SEQUENCE OF FREQ SELECTIONS TO BE MADE AFTER LNDG AT LAX. THE CORRECT PROC IS TO CLR THE RWY; CONTACT GND FOR CLRNC TO TAXI AND THEN GO TO RAMP TWR FOR GATE AND ALLEYWAY INFO. WITH ME CONTACTING RAMP TWR FIRST TO GET AHEAD OF THINGS; THAT THREW ME OFF AND I THINK THE CAPT WAS ALSO THROWN OFF INTO THINKING WE HAD PROPER CLRNC. LESSON LEARNED HERE IS TO ALWAYS STICK TO THE TRIED AND TRUE SEQUENCE OF DOING THINGS. SUPPLEMENTAL INFO FROM ACN 415019: I WAS OBVIOUSLY AT FAULT FOR NOT LISTENING TO HEAR A CLRNC TO THE GATE; INSTEAD OF ASSUMING I WAS CLRED TO THE GATE BECAUSE I HADN'T BEEN TOLD OTHERWISE (BECAUSE OF WRONG RADIO CALL). MY HUMAN PERFORMANCE WASN'T THE BEST THAT DAY BECAUSE I HADN'T BEEN WELL RESTED THE PAST FEW DAYS AND I HAD WORKED 9 OF THE LAST 10 DAYS SO I WASN'T AS ALERT AS I SHOULD HAVE BEEN.