WHAT AM I DOING WRONG???

I CAN'T SEEM TO MAKE MY RENDERING TO LOOK CRISP AND CLEAN AROUND THE EDGES IS THER A TOOL IM NOT
USING OR SOMETHING? OR IS IT JUST BECAUSE THERE CRAPY PICS? THIS IS MY 5th ONE I'VE DONE AND
THEY SEEM TO BE GETTING WORSE EVERYTIME...

HERE'S A COUPLE OF OTHER ONE'S I'VE DONE..I'D LIKE TO GET SOME OPINION'S OF WHAT IM DOING WRONG.