If you have ever played an instrument, you're in luck. I played a lot of guitar when I was younger, so I have a lot of flexibility in my left hand, but not in my right. I've tried different specific exercises, like bending 1 finger at a time. These are OK, but they don't build up much finger strength. As a temporary solution, try bending your fingers at the top knuckle (the one that touches the back of your hand/your palm), instead of the middle knuckle.
With most people, their ring finger and pinkie fingers are tied to the same muscles. I have this problem with my right hand, and have been doing some exercises to make them more flexible, but it takes a long time. Try stretching your first finger toward your thumb, and your pinkie away from your thumb and holding it in that position. That has helped a bit for me. Also, bend your pinkie as much as you can, and hold it in that position as you try to straighten your ring finger (this is hard to do... I still can't do it with my right hand).
Keep practicing as well. It will take a while to gain finger dexterity, and practicing is the best way to gain it. Good luck! Let me know if you have any more questions.