Help anyone?

So I've been working on my line-art style lately and need some tips on how to make it smooth and have the lines thinner. I know its a weird thing to ask about how to make the lines thinner, but every time I draw the lines end up being really thick and dark... O^O

So if any of you have tips out there, or brush sizes to try out please comment! It would be really appreciated!

Thanks!

~Kikira