I need ideas for my small bedroom?

I am 16 and my sister is 8 and we both share a small bedroom. I need decorating and organizational ideas that not only make my room seem bigger, but also help keep away all the clutter that we have going on right now. I hate walking into my room and feeling bombarded with all of my stuff...and it's embarring when I have people over and I know they feel the same way. I need something that not only comes off as grownup and organized for me, but also something fun and pretty for my little sister :) Thanks!