People say that cracking your knuckles makes your grip weaker (not the same thing as cracking knuckles giving arthritis, that is confirmed to be false). If you do that on one hand, try gripping without having cracked your knuckles in a while.
Actually, I have tried to do other things in my left hand, just to see if I can do them. I brush my teeth with my left hand at times, and I can even use chopsticks in them, too. I don't think I'll ever be able to write with the left hand, though. But, if you are set on this, try doing small things first.
One time when I was high, I thought I was in an ambulance dying. Turns out I was just eating sherbert.