DH8 CREW TAXIED PAST GND CTL'S INTENDED HOLD POINT.

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AFTER LNDG AT LGA ON RWY 22; I CONTACTED GND CTL AND RPTED CLR OF RWY 22 ON TXWY E. GND CTL RESPONDED 'JOIN TXWY B; HOLD SHORT OF -- JUST JOIN TXWY B.' I TURNED L ONTO TXWY B (AN ASSUMPTION ON MY PART SINCE I COULD HAVE TURNED L OR R; BUT ALL OUR GATES WERE TO THE L). I PROCEEDED ON TXWY B AND STOPPED SHORT OF TXWY G DUE TO ANOTHER AIRPLANE MOVING ON TXWY G. GND CTL ASKED WHAT WE WERE DOING AND I RESPONDED THAT I HAD JOINED TXWY B AS REQUESTED. GND SAID 'JOIN B; HOLD SHORT OF TXWY F.' I ACKNOWLEDGED TO HOLD SHORT OF TXWY F; BUT I REALIZED THAT WE WERE ALREADY PAST TXWY F; AND GND WAS SIMPLY TELLING ME WHAT THEY EXPECTED WHEN I FIRST CLRED RWY 22. I RADIOED THAT WE HAD NEVER RECEIVED HOLD SHORT INSTRUCTIONS AFTER FIRST EXITING THE RWY. GND CTL SAID TO JUST STAY WHERE WE WERE. EVENTUALLY WE WERE CLRED TO OUR GATE WITH NO FURTHER INCIDENT. IT IS STANDARD AT LGA TO RECEIVE INSTRUCTIONS FROM GND; AFTER CLRING RWY 22; SUCH AS 'TXWY E; TXWY A.' THE ASSUMPTION BEING TO PROCEED ON TXWY E; THEN TXWY A ALL THE WAY TO THE GATE UNLESS OR UNTIL FURTHER INSTRUCTIONS ARE ISSUED. MY DECISION TO PROCEED ON TXWY B; IN THIS CASE; WAS BASED ON PREVIOUS EXPERIENCE. WHEN THE CTLR STOPPED THE HOLD SHORT INSTRUCTIONS AND SIMPLY SAID 'JOIN TXWY B;' I SHOULD HAVE ASKED HOW FAR (TECHNICALLY; I SHOULD ALSO HAVE QUERIED WHETHER TO TURN L OR R). CTLRS NEED TO BE SPECIFIC WITH THEIR INSTRUCTIONS AND PLTS CANNOT ASSUME THAT THEY KNOW WHAT IMPLIED INSTRUCTIONS SHOULD HAVE BEEN STATED.