I have done two lolita costumes. One wasn't very good, but the other was fairly Mana-esque. I still don't feel that I have got the look quite right for my body, but check out my gallery and you can see how my attempts turned out. If you have a similar body build as I do, with wide shoulders and a thick middle, then you can see how the styles of dresses I have tried so far have turned out, and decide if you want to attempt similar ones. Maybe you can learn something from my successes/failures, depending on how you view them.
My personal self-assessment is: Mana eye makeup doesn't work well on guys with minimal eyelid space; puffy sleeves help hide big shoulders and muscular arms; don't hide your legs with a long skirt when your legs are your most feminine asset; don't wear ALL black, because a bit of color or contrast can help draw the eye away from places you don't want people to notice; a few cleverly-placed bows and ribbons can help hide mistakes or flaws; less dramatic, more natural makeup is pretty, while more intensely gothic makeup is less pretty than garish--thus, if you want to feel pretty, go easier on the makeup and include some pinks and purples.