crunches dont work that well on trimming stomach, only toning.
the best way I found that made me lose alot of fat was a month of constant running. I'd do track workouts, because thats what i did.
if you don't know what a track workout is, i'll tell you right here.
run, not jog a quarter mile. after the run, to prevent cramps, grab onto a fence or something low and sweep your legs left to right and back and forth. after you get a little breather, take a 100 meter slow jog. when you hit 100 meters, run 95% of your max speed for 50 meters, jog 50, run 50. do this for 1 and a half laps of a track. after you get another breather, do about 12-14 30 meter sprints at max velocity, 3 minutes in between each other.
do this 4 days a week, with a day of break in between. [ for example: monday and tuesday work. wednesday break. thursday and friday work.]
if you want to be a little toned, incorporate simple ab workouts every second day of workouts. some simple workouts that work good are planks, tabletops, one-legged planks, and side planks. if you got a partner, ask him/her if you can lay down under him/her, grab his/her legs and pick up your legs doing reversed crunches but never touching the ground with your feet. you can also do windshield washers with your legs going left and right to work on your obliques.
i hoped this can help you alot.