A PLT IN AN SMA TAXIED OFF RWY SURFACE ONTO GRASS; MISSING THE TXWY WHILE ATTEMPTING TO EXPEDITE CLRING THE RWY FOR FOLLOWING TFC. THE PLT ADMITTED THAT HE WAS EXCITED DUE TO A GAR THAT HE HAD PERFORMED PREVIOUSLY BECAUSE ANOTHER ACFT HAD NOT MADE A TIMELY TURNOFF.

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I WAS BACK AT ISLIP MACARTHUR ARPT AFTER AN IFR FLT AND ASKED FOR STOP AND GOES TO EXTEND MY NIGHT CURRENCY. ON ONE OF THE LNDGS I HAD TO DO A GAR BECAUSE A PLT WHO LANDED AHEAD OF ME AND WAS ABOUT 4000 FT DOWN THE RWY COULD NOT SEEM TO FIND HIS WAY OFF. ON A SUBSEQUENT LNDG (MY LAST; A FULL STOP) THE TWR CTLR ASKED ME TO LEAVE THE RWY 24 WITHOUT DELAY. IN MY EXCITEMENT; NOT WANTING TO CAUSE ANOTHER ACFT TO HAVE TO GAR; I TAXIED PAST RWY 33L; WHERE I COULD HAVE MADE A R TURN OFF THE RWY; BUT I TURNED OFF THE RWY BEFORE REACHING TXWY B; RIGHT ONTO THE GRASS BTWN RWY 33L AND TXWY B. THE CTLR AGAIN ASKED ME TO GET OFF THE RWY; AND SO I TAXIED SLIGHTLY TO MY R ON THE GRASS ONTO RWY 33L AND THEN PAST THE HOLD SHORT LINE SO THAT I WAS OFF THE ACTIVE RWY 24 AND ADVISED THE CTLR THAT I WAS NOW OFF THE RWY AND ON RWY 33L. I WAS LUCKY. THERE WAS NO DAMAGE OF ANY KIND WHATSOEVER TO EITHER MY ACFT OR ARPT PROPERTY. NO GAR WAS NECESSARY. THE NEXT TIME I AM IN THIS KIND OF SIT I WILL STAY COOL AND CALM AND TAKE THE FEW EXTRA SECONDS TO SLOW UP AND MAKE SURE I KNOW EXACTLY WHERE I AM BEFORE LEAVING A RWY. ALSO; I PLAN TO FLY AT NIGHT MORE OFTEN TO MAKE SURE I AM MORE FAMILIAR WITH THE ARPT ENVIRONMENT AT NIGHT.