I've been getting asked this quite a bit, and after posting the same basic ideas on several forums I've just decided to put it all here so it's easier to reference.
Organizing a benefit is not as complicated as it seems. Understand that everyone wants to help if it's a good cause, and will be glad someone is leading the way. Also remember that you've got all kinds of friends that will get excited and want to help, especially if you're excited. It's contagious. Keep those two things in mind. Now, on to the details.
First, find a venue, nothing happens until you've got a room nailed down. If you can find a place with a PA even better.
It's a benefit, so let the club have the bar, but always ask for a cut of the bar too. Don't give them a share of the door or ticket sales unless they're doing something for you like advertising. If you live in an area with more than one club, shop around to get the best deal. You're going to bring in business and generate publicity for the club, so don't be shy about asking for things. Get the best deal you can.
Now, call all your friends and get them together to talk about how they can help, because you're officially having a benefit once the room is nailed down. It's time to fill in the rest of the details.
Next you need to line-up the musical talent. I'd suggest getting several bands to play short sets rather than a single performer, because what you're after is an event ticket- the chance to see people together that you won't see otherwise. 4 bands laying 45 minute sets is a great evening's entertainment. Also, by getting several good performers on a single ticket you've made that ticket more valuable. Third, you decrease the local competition on the night of your benefit. Really, you want to be selling the hottest ticket in town. Stacking the deck with several talented bands is the way to go.
OK, ticket price. I'd take the normal cover charge and double it as a start. Charge at the door. Really, this is a judgement call. Reality-check this with people you trust, get as much per ticket as you can. Remember that you want to get as many bodies in the room as you can.
Ultimately it all comes down to advertising. Newspapers, Radio and TV all run PSA's- public service announcements. You need a well-written press release and a telephone. Over the phone verify who gets these (numbers are in the phone book, call the main number), fax them in and then follow it with another phone call. Be nice, talk up what you're doing. You need to be persistent, not pushy. Some places, like TV stations, will cut you a deal where they'll give you advertising at a real cut rate. For that you need a budget (see below)
You need to print posters and hang them everywhere. You'll need friends with cars toi help. Saturation is the name of the game, and when you get right down to it you want everyone talking about your show. Saturation.
OK, if you're doing this for the Red Cross or another organization call them today and get them involved. If you're going to put their logo on posters etc, the will need to be involved. They'll also advise about how to handle the money and how to take donations-in-kind (food, etc). Also, because they are a not-for-profit, you'll qualify for the not-for-profit rate if you buy advertising. Again you need a budget, so keep reading.
Still need a PA? Ask the bands, most have their own. Give the band bringing the PA credit for this by making them the host or anchor band. Also, take good care of the musicians, remember that any worth having are pro's and you're asking them to give up a night from the weekend is like asking a normal person do give up 1/2 a weeks salary. Go to cost-co and stock up on snacks for the bands, small things to let then know you appreciate what they're doing. Also plan on each band member bringing a guest. We all love to bring spouses or girlfriend when we're doing something nice for the community.
Next, get an Emcee. Ask the radio stations or TV stations if they have someone that would volunteer , for example. You need a pro to keep things moving, and someone to hawk the raffle items between band sets.
Now, about that budget. Approach (or get friends to approach) the companies you/they work for to get some money. It doesn't have to be much, 500-1000$ will make for a comfortable budget to print posters and buy newspaper adds if you have to. Many companies have matching grants or planning grants that are like free money that never gets used. Cold-call small businessses ask for a couple of hundered dollars in exchange for logo sponsorship (logo on the posters and print adds). With a little bit of nerve and networking you can raise a service-able budget quickly. Or consider donating the operating money if you can spare it. There are ways for you to get a tax deduction, ask the organization you're working with.
OK, here's the real important point. 10$ at the door for 100-200 people isn't much money. If you have an auction table, a raffle, etc, you can easily make 10 times that amount. Again, nerve and leg-work are required, but all you have to do is visit places of business and ask. Bring along documentation that shows you're legit, a letter from the club, etc. Lean on friends to help, they may know people that are store managers at bookstores, etc. Really, this is an easy one to blow by, but I know one benefit that really worked the raffle and silent auction. They set a low ticket price to fill the room and made $25,000 from the merchendise. Wow, yes? You can do that too, it's just leg work
Phew. It's a huge amount of work but it'll all be worth it when you find yourself looking at a room full of sweaty, dancing people all there for a good cause.
Oh, one last thing. Always remember to say thank you. It's so basic. Send thank you notes or call everyone that helps. Send thank you cards to the businesses that donated stuff. It's polite, and (ha ha ha) most places will hang them in a very public place. It's recognition for them, and great free advertising for next year,m when you start all over again....