ALL ABOUT TOMBOY

Don't want to be a tomboy anymore? It's simple but you have to make sure you want to do it!

Steps

Start off with small changes, don't do anything too drastic at first. Like if you keep your hair pulled up most of the time then wear it down. Or try sports-appropriate makeup such as lip gloss.
Start doing bigger things. Like if you wear glasses get contacts or add subtle highlights to your hair.
Go shopping. Go to places like Abercrombie and Fitch or Hollister or where ever all the girls LOVE to shop. If you hate shopping, buy a few key pieces that will last you for a while.
Wear make up. Don't go overboard! Mascara, eyeliner, and lip gloss will do fine.
Try to befriend more girls if all of your friends are guys.
hang with mostly girls

Make sure you want to change. Be ready for anything you have to do. It doesn't mean that you have to give up your sport, just be more feminine.
Don't change fast! Take your time. If you do all this over a weekend you'll look weird to other people.

Be prepared to be viewed as a wannabe. Just follow these instructions carefully and you shouldn't.
Many studies suggest that tomboyishness is forged in the womb (check out wikipedia for references) and is inherent in one's character, so be careful trying to become what you're not. There's nothing like being yourself.
Having guy friends has it's advantages when you're a girl. Guys can be easier to talk to, and generally don't gossip. Also, if you have more guy friends, you have way more potential boyfriends when the time comes that you want one.
There's nothing wrong with being a tomboy, and a lot of nice people like will like you for who you are no matter what, so if you're changing for a boy, and not for yourself, you'd just be doing it for nothing.