To start with, if you plan on hosting a backyard luau, send out Hawaiian themed invitations, and inform your guests that you are having a Hawaiian Luau and ask them to wear Hawaiian themed clothing if possible.
Next you will have to get all the things you will need for a luau, such as enough lei for all your guests. These are easily found in party stores.
You'll want some decorations that are reminiscent of Hawaii, such as tropical fruit and flower themed decorations. Again, these are easily found at most party stores.
Create tropical centerpieces from your decorations, as well as fresh fruit, such as pineapples and coconuts. These table centerpieces can really set the mood for a great luau.
For the actual Hawaiian Luau you may want to see if you can hire a hula dancer to meet your guests, or talk one of your friends into the task. Of course you'll also want some Hawaiian music playing throughout your party.
Aside from the atmosphere, there's the food to consider, and you'll want to serve some authentic Hawaiian food and drinks. Some ideas for your dinner include, lomi lomi salmon, huli chicken, and of course for drinks, there's mai tais, and blue Hawaiians.
Having your own backyard Hawaiian Luau is fun, and your guests will love it.