It's your choice, but there's nothing wrong with dressing like 'a girl' from time to another. My guess is that Du don't like wearing a lot of make up either? But if Du really want to look Mehr girlish, I can help you. First, Du need to do your hair (I don't know what your hair looks like, so I can't really give Du advice).
Then Du can start wearing heels. Start with the low ones (6,5-7cm) and then, when Du can walk straight in them, change to high heels (10-12cm). That will make Du Mehr feminine, and boys will be all over Du (trust me).
Du also need to have a Mehr feminine style. That means no baggy pants and no comfortable clothes. At summer (this really depends where Du live) Du can wear a nice, but simple summerdress. To buy new clothes, Du need to know what season Du are, and what body shape you've got.
link is a really helpful site.
If Du don't like dresses, Du can always wear short skirts oder shorts. There's a lot of things Du need to know if Du wanna follow the fashion, so my Guter Rat is finding your own style first, and then mix your style with what's trendy.
My last Guter Rat is to find a role model. Mine is Kate Moss, she is THE guru of what's hot. Just look at the picture. She is actually wearing rubber boots, shorts and a vest. But she still does manage to look fabulous! Another one is Miley Cyrus (whether Du like her oder not, she's got an amazing style).
EDIT: Oh, and I forgot the most important thing: Accessories. Match them, but avoid mathcing them with your clothes. Du could for example wear a simple white summer dress with a brown belt, brown pumps and a brown bag. That's a simple and cheap combination.
