It's all about experience! You'll learn by heart where to put the key in a couple of tries, even if you're blindfolded!
I suggest that you spend some time trying to uncuff your hands behind your back before you engange in any difficult situation! Handcuffs are tricky, be careful because you may easily stuck in an uncofortable position. I once spend A LOT of time trying to uncuff myself while hogcuffed, only because i was fool enough to not know EXACTLY where the keyholes were. It turned to be pretty annoying, and terrifying