Inspired by suggestions from Hemant Mehta.
For all of the faults in theology, Christians have a lock on charity work. When someone thinks of Christian kindness, I doubt that they imagine brainwashing children to fear a non existent Hell and a deity who watches every move and knows your thoughts. Instead, images of soup kitchens, food shelves, homeless shelters, Habitat for Humanity, even sandbagging ahead of a flood are all things churches are known for. Why aren't the same things associated with atheist kindness?
Atheists do give time and money to charity, but how come no one knows about it? I think that atheists are more concerned with helping others then getting recognition for efforts. The side effect of this unselfishness is that efforts of atheists are ignored. Also, atheists don't tend to organize well. While there are great freethought groups out there, an organization of 300 members can have trouble getting enough volunteers to help with a road side cleanup, but it's members on their own volunteer at homeless shelters, animal shelters, collect food for food shelves, donate blood, and help sick children. While this helps humanity as a whole, it does nothing to rid the stereotype of atheists as a bunch of intellectual nihilists who have turned their back on humanity.
So, where to start? First, you need an idea, then you need to promote, promote, promote. Christians use newsletters, fliers, sermons, posters, calling members, television and radio, and the Internet to get their messages out. Any group can get a few people together to brainstorm volunteer ideas. Choose your events carefully. Decide if you want to have an event which costs money, such as donating new toys to kids, or something which takes time, like stocking a food shelf or raking lawns. Many atheists aren't wealthy, so events which involve time rather then money fit well. One way to get around this, is to go door to door asking for donations for your project.
Most organizations have a newsletter, so start promoting your event early and often. That article on the ontological proof for God can wait until next month. Make up fliers and put them up in public places. Coffee shops, grocery stores, and libraries are great places for nearly free publicity. Atheists don't have sermons, but they usually have regular meetings. Take some time, or a whole hour, talking about different volunteer opportunities in your community that you're going to participate in. A variety of events makes sure more people can participate. Not everyone can donate blood, or make it to a food shelf on a weekday. Start a mail list, or an email list of interested people, so they are always up to date on the latest opportunities. Use social networking tools, like Facebook and MySpace or Meetup.com to post invitations to volunteer events. Oh, and be prepared to offer something to your volunteers for helping out. Food is a strong motivator. Use your website to let members know about upcoming events. You can use a Google calendar that people can subscribe to and keep your events there. It's simple to update, and easy for people to stay up to date.
Not every atheist group has access to television or radio programs, but sending out press releases to news papers, radio and television stations is an easy way to get some publicity. This is especially effective if your story is interesting and unique. You should get to know the reporters at your local news papers. Often times, someone will be more sympathetic then others to print pieces about you, and it's good to know who that is. A press release doesn't have to be elaborate, but should have enough information to entice a writer. If all of your efforts to get the word out have failed so far, the Internet is still a great resource for promotion. Email atheist bloggers, conservative and liberal bloggers, any popular blogger who may be interested in your story. They can have more eyes then a local newspaper, and that type of promotion can lead to news stories. Contact groups that produce podcasts and see if they need a guest. If your story is interesting, most producers will like it.
By using resources you already have, and spending a little bit of time, you can pull people together, make a difference in your community, and promote atheists as positive people.