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