Party Tips???

Hey- I`m 15, and i`m throwing an end of the school year party in a few weeks... The invitees are freshman and sophmores (14-16 years old) and mix of girls and guys --about 50 or so--.... I need suggestions for food, decorations, games- Whatever anyone can think of. The party will be from around 630 to 11, so we`ll hang outside and inside. But Im not sure what to Do with So many people! This is my first Big party, so if you have any ideas- PLEASE HELP!