Hiya! Saw this on SEOmoz’s twitter account. Your enthusiasm and desire to learn more about best practice is marvelous.
Here's my two cents:
My understanding is that you have signed up for Facebook, Twitter, Youtube, and a few more. It's great that you want to be more social, but sometimes companies get too gung ho about social media and start everything all at once. As you've already realized this is a cart-before-the-horse type situation.
So take a step back. Before everything else, you need to think about what you hope to achieve through your social media. Have defined goals: driving traffic, raising sales, gaining a reputation as an expert in your industry, all of the above.
Then you have to think about the online community you are joining. Who is your audience? What content or information do they want and need? What will attract their attention? Of that, what do you already have to offer?
When you're doing business to business social outreach, you would share content that other businesses find useful, clever, or fun. This includes not only content they'll enjoy personally or professionally, but also things that they can share with their own clients.
Only once you've gathered or brainstormed this information do you start thinking about which social media platforms best fit your needs. Each social media network is useful, but they each have unique strengths and weaknesses. Be cognizant of these as you decide how to disseminate which content to which audiences. What you do for Facebook is not what you do for Twitter is not what you do for LinkedIn. Make sure you do your research and that you are aware of the ebb and flow and flavor of your audience as you build a following.
And of course, none of your lovely social efforts matter if no one knows that you're making said lovely social efforts. Be sure to put your social media buttons on your site.
There's obviously a lot more that goes into this and a social media consultant/strategist can help you work it out. But these are the bones as we see it. They're really not that different than any other kind of marketing: Have goals. Know audience. Stay aware. Eat chocolate. Rinse. Repeat.