i can already play good with my right hand but when i start using both hands, one hand wants to imitate what the other one does.
do little finger exercises or do contrary motion scales e.g. cmajor R.H cdefgabc L.H cbagfedc at the same time then practice the left hand part of the music you're trying to play and slowly bring both hands together one bar at a time
i would first learn each hand separately. then when you're ready to do both hands, literally do one bar at a time, going reeeaaallllly slowly. yes, it does take a while, but it's a nice result. (the reality is: practice makes perfect!)
Practice practice practice (: get a professional to help to show you how to use both hands, and if you know it really well it will just tale practice to use both hands. I used to type with only my right hand but now i use both lol
Practice one handed until it's almost perfect then practice the other hand until it's perfected then try to put both hands together.