This is the comprehensive guide to kicking your little sister out of your room. It is rated in stages, the lower the stage, the less trouble you will get in (in my experience).
Stage one
Ask nicely.
It might hurt your pride, but it is sometime effective. example: "Maggie, Lizzy wants to be alone for a little bit, please leave"
Stage two
Ask no-so-nicely.
"Maggie, get out of my room!"
Stage three
Bribes.
Offer her chocolate, or some other form of candy.
Stage four
Heaver bribes.
Offer her a hair brushing, or offer to paint her nails (It takes a little more time, but she will leave you alone eventually)
Stage five
Threats.
"Maggie if you don't out of my room I will tell mum and/or maul you!"
Stage six.
Throw her.
Dragona you should have no problem with this stage.
Stage seven
Give up for a little bit, then start at the top again.
Disclaimer: It is so not my fault if you get in trouble, have to go to the hospital, mum yells at you, etc...