A LOW TIME C172 PLT TOOK OFF FROM TXWY D; INSTEAD OF RWY 30 AT SUA.

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I LANDED AT WITHAM FIELD (SUA) FOR A TAXI BACK TO THE RWY FOR IMMEDIATE DEP. ATC TOLD ME TO PROCEED TO RWY 30 WHICH I HAD LANDED ON. I PROCEEDED TO A POINT WHERE I SAW A SIGN FOR RWY 30/12 (INTXN D). I TURNED L TO PROCEED TO THAT AREA. I CALLED THE TWR AND RPTED THAT I WAS AT RWY 30; INTXN AT TXWY D. I WAS CLRED FOR TKOF WITH L OR R TURN AT MY DISCRETION. UNFORTUNATELY; I WAS POSITIONED TO TAKE OFF ON A 340 DEG HDG (IE; I HADN'T TURNED ONTO RWY 30 AS I SHOULD HAVE). I DEPARTED ON A TXWY D WHICH PARALLELS RWY 34. (I AM FAIRLY CERTAIN I WAS DEPARTING ON THE TXWY; AS OPPOSED TO RWY 34; BECAUSE TO GET TO RWY 34 I WOULD HAVE PROCEEDED PAST AND NOT TURNED L ONTO TXWY D.) THERE ARE SEVERAL REASONS FOR THIS ERROR. FIRST; I SPENT LITTLE TIME THINKING ABOUT OR STUDYING ARPT SIGNS AND MARKINGS PRIOR TO MY FAA EXAMINATION. IT SEEMED LIKE 'OBVIOUS' STUFF; SO I DIDN'T FOCUS ON IT. SECOND; ONE GETS VERY USED TO FLYING OUT OF THEIR HOME ARPT; AND OTHER PLACES PRESENT DIFFERENT ISSUES. ALSO; I'M WONDERING IF THE FAA EXAMINER; BECAUSE I DID SO WELL ON THE ORAL EXAMINATION IN THE OTHER AREAS; FELT I DIDN'T NEED TO BE QUIZZED ON 'EASY' STUFF. ALSO; MOST OF MY TRIPS HAVE INVOLVED ONLY TOUCH AND GOES; SO IT WASN'T OFTEN THAT I HAD TO MANEUVER AROUND A FIELD. IN FACT IT WAS RARE. THE POINT; HOWEVER; TO ME IS TO THINK AND LOOK WHILE ON SURFACE AREAS. I CERTAINLY LOOK FOR TFC BUT KNEW; EVEN BEFORE THIS INCIDENT I NEEDED MORE KNOWLEDGE AND CONFIDENCE WHILE POSITIONING ON THE FIELD. ALSO; THE TEACHING SYS WHERE IT'S A DIFFERENT INSTRUCTOR EACH LESSON; FOR SOMEONE LIKE ME; IS TERRIBLE. YOU CAN EASILY SLIP THROUGH THE CRACKS ON A GIVEN ISSUE BECAUSE THEY ASSUME YOU KNOW IT. I HAVE; PRIOR TO THIS INCIDENT; CONTINUED TO READ AND LEARN ABOUT AVIATION SKILLS. ARPT MARKINGS WAS ON MY SHORT LIST AS I HAD A MARKINGS PLACARD ON MY DESK THAT I MEANT TO STUDY; BUT NEVER QUITE GOT TO IT. SINCE THIS INCIDENT; I HAVE BEEN EXTENSIVELY EXAMINING ARPT MARKINGS AND SIGNS AND THINKING ABOUT SURFACE MOVEMENT. I KNEW I WAS ON THE WRONG HDG (COMPASS-WISE) BEFORE DEP BUT: 1) WASN'T FULLY CONVINCED I WAS IN THE WRONG AREA; AND 2) PROBABLY WASN'T CONFIDENT ENOUGH TO BE PROACTIVE AND REPOSITION OR CALL FOR ASSISTANCE. BUT; OBVIOUSLY; THAT I DIDN'T EVEN CONFIRM THAT I WAS ON A RWY IS THE MOST DISCONCERTING TO ME.