I'd love to help.
Although, I'm probably not the best person. There are far more capable people on this thread than me, but I know a thing or two.
I suppose the first thing would be to start looking at some nice pencils and tortillions. Not that I'm saying you don't have nice pencils, but it does make somewhat of a difference when you start using pencils like 2B, 6B, etc. You can normally find them at craft stores.

Then, practice your shading. There are probably a million different books out there that can help, which is what I did for a while (though I'm mostly self-taught). When I couldn't figure something out on my own, I looked towards a book I got for school a couple of years ago and that pretty much got me out of tough spots.
Practice as well. Like, seriously, practice. I can't stress it enough. o_o It might be a bit tough for you to adhere to the whole drawing realistically, because of how well you are drawing your Monster high and cartoony stuff. But that should stop you, I honestly don't know hwy it would.
Does that help at all?
Is there anything specific you need help with?