Every time a new digital communications medium becomes popular, along with ushering in a wave of new users, it also ushers in a wave of complaints about these users as they behave in ways considered inappropriate or impolite by more experienced users.

With email, reviled behaviors include the sharing of old jokes or long discredited urban legends with everybody in your address book. With Usenet and other online discussion groups, it includes the asking of basic questions that are already answered in the FAQ that first-time users are supposed to read.

Social networking sites such as Facebook (www.facebook.com) and LinkedIn (www.linkedin.com) are among the newer communications media. They're now reaching a critical stage of popularity in which the upsurge in new users is creating widespread complaints about the behavior of these users.

Facebook claims to have more than 140 million active users worldwide, while LinkedIn says it has more than 30 million registered users spanning 150 different industries.

Here are some suggestions about looking your best while social networking for business, pleasure, or both:

1. Choose your profile picture carefully. Sites such as LinkedIn may be used more for business and professional purposes, but social sites such as Facebook and MySpace can affect your business or professional reputation as well.

2. If you're in junior high school, a goofy Facebook picture of you bending over with your head between your legs peering backward won't cause you any harm. But if your picture may be seen by someone who could hire you, promote you, or buy a product from you, think about the image you're putting out there. It doesn't have to be totally buttoned down, but you shouldn't let your hair down completely either.

With LinkedIn and other professional sites, consider spending a couple of hundred dollars to hire a professional photographer if you or those around you don't have the necessary skills. Your picture is your first impression, and you don't have to be a model or an actor for it to matter.

3. Write your profile carefully. As with any kind of writing, you'll come across best if you think about who you're writing to. Many people don't take full advantage of Facebook's privacy settings, which let you control who sees what information about you. You're probably better off exposing the inner you to a select group of friends and family members than the entire online world.

With LinkedIn as well as Facebook, be honest. You want to put your best foot forward, accentuating the positive, but resist the pull toward vanity and exaggeration. Unlike a resume, your LinkedIn profile may be seen not only by prospective employers who don't know you but also by your current supervisor and work associates.

4. Think carefully about who you're "friending" or adding as connections. Online social networks by definition are designed to expand the number of people you can connect to. But don't assume more is better in every situation. It can make sense to be strategic here.

On Facebook, some people like to boast of having hundreds of "friends," but just because people are friends of a friend doesn't mean they would make a true friend of yours. You have every right to ignore requests from people you don't know or can't recall.

Sometimes here, however, a good strategy can be to sit on such requests for a couple of days in case your memory of the person returns or to give you time to search through your email outbox to see if you've ever exchanged emails with the person. Also, if someone friends you online, don't expect that the person will automatically be receptive to extending this virtual social relationship to the physical world.

Similarly, on LinkedIn some people brag about having hundreds or even thousands of connections even though the service was designed with the philosophy that people should know one another before establishing a connection. If you try to establish too many random connections and too many people click on "I don't know" with reference to you, you can be blocked from using the service.

5. Think carefully about what you're communicating. Not everybody in your Facebook network may be interested in how your date went Saturday night, but they may be interested in why you decided to buy a digital single-lens reflex camera. Keep the private private.

Much of social networking etiquette is common sense, common courtesy, and restraining from getting too carried away with the common ways that these services can extend your social reach.