Do as MUCH as you can in advace.......food, table decorations, setting up displays, etc. Make yourself a list and prioritize.
2. If there are any family members who'd like to help, like a grandparent, even witth things like picking up paper goods, etc. LET THEM!
3. Table displays are the best and easiest ways, I THINK, to showcase her school years, volleyball, of whatever....pictures, trophies, medals, etc. make sure to include something fromt he college she will be attending so that people know where she'll be going. i.e. if she's got an article of clothing, bumper sticker, etc from where she'll be attending, put in on the display, as well,
4. Make sure to include some pics, etc of her childhood because there will be people who've only known her for far less than 17 or 18 years.
5. you can go to Wal-Mart and get display boards that are bi-fold or tri-fold if you want things that are vertical as well as flat on the table. ...makes a nicer display and you have more versatility. Use colors of the school she's graduating from, but include the colors of the school she'll be attending...crepe paper, poster board, gems, confetti, etc.
6. No "rule" as far as the sides are concerned. Just keep in mind the time of day, ie.e if it's round lunch time, you'll want/need more than if it were going to be at 3 or 4 in the afternoon. How many other kids are hosting their parties at the same time? If several others are, don't go overboard, the kids drift from house to house and won't always eat or eat much at every house. Obviously, family and family friends will stay there, but preparing for the kids attending is something to consider, as well.
7. Don't go overboard w/ hot food. It's an extra effort to keep it hot, unless you're using warming trays, etc to keep them that way. Stick w/ more finger food, appetizer type foods, if you don't have that option. Crockpots can always be a HUGE help, here.
8. One of the FAVORITES I've prepared for all kinds of occasions is a Soutwestern Tortilla pinwheel. Take 2 blocks of light cream cheese, softenined, a package of taco seasoning, a jar of salsa ( I prefer the corn & black bean and try NOT to get a runny salsa) and a package of light Mexican cheddar. combine those and spread - not too much- on a LARGE tortilla. If you use the large ones, it goes faster. Don't use too much filling because when you roll them, the excess filling will ooze to the end and you'll have to take it off anyway.
Anyway, roll the tortilla up and then slice the roll into pinwheels 1 -1/2 to 2" think or to your liking. THESE GO FAST!!! Best of all, you can prepare them a day or two in advance and keep them ready to serve.
Veggie trays and dip are always a good option, as well. In season fruit (and dip, if you choose) is another excellent one......strawberries, grapes, kiwi, fresh pineapple. There's even a company called EDIBLE ARRANGEMENTS that makes arrangements out of fruit, if you wanted to use something like this as a "centerpiece", as well.
Hope this helps. I've done a TON of this stuff!