From my experience with more kinds of luaus than I can remember, I made a list of important tips about how to have a luau whether you are in Hawaii or in your own back yard. First, there is not really a set of rules for a Hawaiian Luau but we would expect to see at least a few of these things. Especially for Luaus not in Hawaii, the more of these ideas you can use the better. You will have a lot of fun getting ready for the party and your guests will have a lot of fun with the decorations, food and games.
LOCATION LOCATION LOCATION - Once you figure that out you can start to set the stage.
Decorations -
1. Flowers
A luau without flowers? Nevah!
Most of the time we decorate for every party with lots of flowers and leaves. We might decorate items with shells and kukui nuts too. But flowers and leaves are the main decoration that you should have plenty of. If you aren't on a budget you can buy real Hawaiian flowers including the rare ones from your local florist. We like birds of paradise, calla lilies, gingers, orchids, and heliconias, but you can use any bright colorful flowers. If they smell good too that's better. We tie them on posts, put them on tables, wrap them around things like napkins, and wear them in our hair and around our neck, head or ankle with a lei. We like big arrangements!
This guy is a pro! You can learn what our flower styles look like. For some reason he didn't make an embed code so part one is here http://www.youtube.com/wa...
Part 2 -
Leis
If you have no other flowers but leis, you're still good! At least the hosts and guests of honor should get or wear leis if not every body. You can either have them ready when guests arrive or set up tables with the flowers, strings and needles to let guests make their own. For a lot of parties this is one of the favorite things for guests to do.
If you need to keep your budget lower or don't have a lot of flowers around your house, you can add leaves to the lei table and tell guests to roll them up and sew them across the center between each flower. If you are really, really on a budget like me you can tell them to make all leaves except a few flowers. If you want traditional orchids some of the local nurseries might ship them to you direct. Men like to wear both kinds and so do women. It's all good!
2. House Decorations
Set the mood!
Your luau should be mostly outside so these can be used indoors or out depending on your set up. I found these you tube videos that have the kinds of things that we might make for a luau party. You can also buy Hawaiian theme items at party stores and dollar stores.
These girls have a cute idea for an invitation and show how to decorate a pineapple. You should definitely have pineapples in your table decorations. I like to make a string of flowers and wrap it to the top leaving only the leaves and a little bit of the yellow showing.
This is how to cut a pineapple spiral. It is better if you stick grapes or other fruit in the cut outs. https://www.youtube.com/w... (Edible decor -ONO!)
I like these colorful paper bag decorations and another way to use small paper bags is to decorate them and put a tea candle in a glass inside. You can use these on tables or line them up anywhere but they look especially nice along your driveway or sidewalk. Don't catch anything on fire. lol
Luminary candles in a bag
Tikis
If you are good with a chainsaw you can make your own tiki! It doesn't take that long if you have the tree trunk. Don't cut off any body parts! lol If you can't make a real tiki maybe you can find tiki candles or masks. And if your luau is going on into the evening, don't forget the tiki torches and have a few extra wicks and oil on hand.
Food
The main attraction!
For authentic luaus you should cook in an imu. If you don't know what an imu is or how to make one this video is really good at showing it step by step.
This video is good to show how to make a mini imu just for your Kalua Pork and if you want authentic luau, Kalua pork is on your menu. Or use your imagination to duplicate this kind of cooking in a crock pot, stove or grill but I'm telling you it won't be the same. 
This imu is only about 2' square and 1 1/2 ft deep.
What ever you use on the bottom layer, and banana stalk is awesome, I like a few ti leaves on top before the food and more ti leaves on top and then add the rest of what you have. (Green ti only) Florists can order them or you might get local Hawaiian florists to ship them to you directly. About ti - http://www.primitiveways....
A modern day luau will probably have all of these: Kalua pork, Lau lau Mac Salad, and of course two scoops of white rice per plate! This food group is known as "The Hawaiian Plate." Hawaiian Plate lunch restaurants are prolific throughout the islands. This guy cheats the lau lau and makes collard greens which is just slightly less old school traditional, but shows an easy way to make the other Hawaiian favorites in your kitchen. He also shows you how to make a a nice plate presentation with these foods wrapped and tied up in a banana leaf.
Entertainment
Must have music!
If it's a blow out, hire professional hula dancers and musicians. But if you want an equally fun alternative there are a lot of options.
At the low end of the preparation and cost scale would be to play Hawaiian music in the background. For some parties this is still a major hit and no one will be disappointed.
If you want to take it a step further, gather up any percussion instruments or noise makers that you have and ask guests to bring any they have. You might consider if buying little Hawaiian style gourd shakers is worth it depending on your guest list or occasion. Start or assign someone to form a percussion (drum) circle and keep beat with the music or make up your own rhythms.
A lot of communities even on the mainland have Hawaiian Councils, Hula classes and other groups that you might contact to see if someone would be available to come out and teach your guests about hula gestures and a little dance. Guests could also learn words and meanings. Off of this you can use your imagination to extend games such as with the use of the Hawaiian words or gestures in word games.
If you are a musician then learn a song to play for your guests, or if you are a singer you can probably find the music to a song on some of the karaoke sites to play while you sing. If you have musician friends they might be enticed to learn a Hawaiian song for your party or provide free entertainment. I've been to as many luaus that had live music as not so it isn't a necessity. But the many luaus I attended where one or more people showed up with a guitar or native drums, who then occasionally jammed for the rest of us were memorable. But then in Hawaii anyone who couldn't really play wouldn't show up to ruin a party either so depending on your guests invite guests to bring instruments carefully. lol
If you want a party with games or can talk even a couple of people into it to entertain others, (lol) any game you can find that uses fruit would allow you to play with things that can be used in your decor.
I will mention lei making here again in the event you want to offer that as an ongoing activity rather than hand them out but guests of honor, for example at a luau to celebrate a birthday or graduation, should not have to make their own.
What to wear
It's a luau, be comfy!
If it is a dressy occasion, Hawaiian shirts for men and floral dresses for women. A causal occasion is usually Hawaiian shirts or T-shirts for guys with board shorts, jeans or causal cotton pants. Women might wear, sarongs (pareros) with cute tops, shorts with a bright of flowery top, jeans or floral dresses. Comfortable shoes at any occasion and some you can kick off at casual gatherings. Ha! Actually if its casual wear what you want! This all depends on how authentic you are trying to be or if it matters to you. I'm only providing suggestions in the event someone has no idea about what would be "normal" to wear at a Hawaiian luau.
What to Bring
#1 item every guest must bring is Aloha!
Again, for all but the most formal occasions, guests may consider it to be proper and welcomed to bring a food dish, drinks, a host/hostess gift such as a tiki torch and fuel, a serving plate, flowers, a game, an instrument or anything that you feel is appropriate to contribute. Its all about the act of giving and participating in the gathering but also don't feel bad if you don't bring anything. but yourself, an appetite and lots and lots of aloha! It's a luau, EH, RELAX ALREADY!
What is aloha?
Now all you have to do is HAVE FUN!
Sure, I'll come to your luau!