Don't put things online that you wouldn't be comfortable seeing again one day. This may be a particularly hard lesson for people who have not entered the professional world, but hope to one day. They've grown up with technology as a trusted means of self-expression.
There's no back-patting for companies that have Twitter accounts. You need to create meaningful interactions with real people, and you need to find a way to scale your particular method as your network grows into the tens of thousands.
Whether you're an American icon or a fatigued social media stalwart, one thing is clear: We are never really alone, or left alone, anymore. Our society has succumbed to a full-on state of co-dependence.