Starts Then Dies

SOMETIMES WHEN I START MY CAR WEATHER IS' WARM OR COLD IT DIES SOMTIMES. I THINK THAT IT STARTS THEN IT DIES AND THEN I HAVE TO CRANK IT OVER A COUPLE TIMES THEN IT STARTS, AND WHOLE ENGINE SHAKES(KIND OF EMBARASSING). BUT IT ONLY DOES IT SOMETIMES, BUT SEEMS TO DO IT MORE AND MORE OFTEN. WHAT COULD THE PROBLEM BE?? THANKS