13th Birthday Party

Heyy, im havin my birthday soon, the beginning of september and i was wondering if i could have some ideas from you guys?!
Im inviting about 25 people, and all ive got planned so far is music and food.. But i need more ideas..
We have a Big garden, and a pretty big house aswell, but i wanna stay out in the garden.. So if anyone has any out-door party games.. Or indoor ones that can be played outside.. I would really love to know! the only this is that i dont want anything too messy because my mates will be sulking that theyve got dirty.. Ect ect..
So please help me!! any ideas will be appreciated!
Thanks! Melissa xx