It's your choice, but there's nothing wrong with dressing like 'a girl' from time to another. My guess is that you don't like wearing a lot of make up either? But if you really want to look madami girlish, I can help you. First, you need to do your hair (I don't know what your hair looks like, so I can't really give you advice).
Then you can start wearing heels. Start with the low ones (6,5-7cm) and then, when you can walk straight in them, change to high heels (10-12cm). That will make you madami feminine, and boys will be all over you (trust me).
You also need to have a madami feminine style. That means no baggy pants and no comfortable clothes. At summer (this really depends where you live) you can wear a nice, but simple summerdress. To buy new clothes, you need to know what season you are, and what body shape you've got.
link is a really helpful site.
If you don't like dresses, you can always wear short skirts or shorts. There's a lot of things you need to know if you wanna follow the fashion, so my payo is finding your own style first, and then mix your style with what's trendy.
My last payo 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 you like her or 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. You 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.
