Does anyone have curveball advice?

I'm 16 and am more of an outfielder, but I do pitch occasionally. Right now I throw a 4 seam, a 2 seam, a change and curve that has good movement, but due to my 3/4 arm slot, tends to run a lot, and only drop a little. I'd like to throw one that is more 12-6, wether I add it to the arsenal, or scrap the curve i have now in favor of a 12-6. The problem is i can never seem to throw such a pitch. I have tried every grip i can think of, including that of a knuckle curve, but i can never seem to get on top of it; it just hangs up there. Another question: how can I get more spin on either of these pitches so it is more disguised? I've faced people who throw curves that are hardly recognizable because they are so tightly spun, but I can never seem to do that. Thanks for anything you can contribute.