While the networks are diverse in their approach, common netiquette is emerging that is particularly important when using them professionally:
Explore a network before diving in. Lurk (or, in Twitter, "follow") for a bit to learn its personality. Twitter is about being noticed for having something interesting to say. And while the lines are blurring, Facebook remains a mostly horizontal world where users usually want to connect with more friends and fewer bosses, underlings, or even colleagues. LinkedIn, on the other hand, is as much about helping those below as seeking out those above.
Fill in your profile. Describe yourself in words that a recruiter would use in a search for specific talents, experience, or accomplishments. Massage your bio as opportunities change. Link to your blog or to a website that showcases your thoughts, work, or at least a longer biography.
It's about sharing, not selling. Shameless self-promotion is as distasteful online as it is at a cocktail party. Adding wit or wisdom to a Twitter conversation gets noticed. Approach other members prudently and almost always through a mutual friend or contact. Offer them help, such as a lead you've gleaned from networking. Or maybe ask a recruiter who has a job that's not quite right for you: "How can I help in what you're currently looking for?"
Know they're watching. Professionals need to present a sober and thoughtful personality. Employers increasingly prowl networks to find new candidates and to eliminate existing ones. A key source of income for LinkedIn is from companies that pay to get access to more information than is available to the vast majority of free users. That can work in your favor or not.
Search for people, not just for jobs. Target companies of interest, and find friends of friends with responsibilities similar to yours or in positions you seek. Approach them through a referral. Try to have something to offer, perhaps industry insight or a news item. It's crucial to have someone inside who can push a résumé forward from the stacks of online applicants.
Get creative. Learn all you can about someone you're meeting for the first time, particularly anyone who's interviewing you for a job. Research your competition: If you have names, knowing their backgrounds can help shape the emphasis you put on your strengths or experience. Keep in mind, too, that competitors will be looking at your profile. And while still employed, don't compromise your company's information or strategy.
Understand privacy. It's growing more awkward as professionals in Web networks increasingly mix work and fun. Many of the sites have privacy settings that can control which friends can see what. Learn and use them. Then you can confidently accept your boss's friend request.
Join in. Most networking sites have groups that focus on particular fields. Or you might find a Facebook group for former colleagues at a particular company, which can be an invaluable resource for staying in touch after a round of layoffs. Discussions related to your field, such as Q&As on LinkedIn, are a great way to get noticed by others who share your interest.