Like others have said, C-rails are just a balance between speed and leaning. I first learned on a rail with my tails in inside the curve but either way is fine.
If your tails are inside the curve, think of sitting in the backseat as you land on the rail. I also think of putting my front should down toward my front ski because the natural inclination is to lean back and not completely get into the rail. Make sure you get completely sideways to the rail too.
If you're leaning forward into the C, pretty much just make sure you get sideways and lean forward.
As you begin doing them, you figure out the speed/lean ratio. If you're falling inside the C, speed up or lean less. If your falling outside, slow down or lean more. Hope that helps.