The first thing that comes to mind is a simple one -- be nice to people. It's something we often forget while running hurriedly around town, absorbed with our own business -- but it's important, especially when something happens that makes us think that we're all in this together. Little things can mean a lot.
Something else that's important in times like this: do what you normally do. The aim of any sort of terrorism is to make people change what they do and be afraid -- so let's not give whoever this was the satisfaction. Sure, there's more security in some places now, but we can still go about our lives like usual. Let's not be afraid. (The Post has more on this.)
And a big one: do something good for other people. Aside from just being nicer (and more aware of being nicer,) let's work to help others. The Red Cross is always a great organization, and the Boston and DC area chapter could surely use your help. There's a lot of great groups in Columbia Heights and around DC that help people and do good work too -- go check into them. Off the top of my head, there's the Latin American Youth Center, which works with local kids, 826DC, a tutoring group for kids and Words Beats and Life, which puts on art and music programs for youth. Lots of churches And there's many more groups I'm probably forgetting -- leave your favorite in the comments!
Around town, there's great groups like Food & Friends, which delivers meals to people with AIDS, cancer and other illnesses, Bread for the City, which helps low income families, Higher Achievement, which works with middle school kids, and many, many more.
It doesn't even have to be organized. Help out a neighbor. Organize a neighborhood cookout.
Times like this make me think how important life is -- our family, friends, loved ones and community. Let's do something, be good to each other, and make things better. Let's not let terror beat us.