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