The Web site did the work of finding people for him, providing a list of likely connections by searching its own database of people who had overlapped with him at past jobs. All Mr. Lunn had to do was review the list and select contacts he wanted to add to his network.

“Some of them are now doing very useful jobs,” he said.

That’s the point. You don’t have to fear you’ll be perceived as using them; they are on the site for the same reason. They might well intend to use you.

Even so, don’t go crazy trying to connect with everyone you brushed past in the hallway 20 years ago, or friends of friends. Too many people can weaken your network.

“We try to discourage promiscuous linking,” said Kay Luo, a spokeswoman for LinkedIn.

But don’t be afraid to network strategically. You want to connect to people who can get you jobs. “People usually invite up — people above them in hierarchy,” said Ms. Luo. “When you’re talking about a professional network, quality is so important.”

So if the No. 1 tactic is to connect with people who are useful and successful, how do you make sure you’re one of their worthy connections? There are a few helpful approaches.

Ask for recommendations. Mr. So, who so quickly parlayed his connections into job offers, said that having updated recommendations with his résumé on LinkedIn was crucial to being noticed.

“The only way to get recommendations is to go out and ask for it,” Mr. So said. “It’s kind of a weird system. I typically go to my bosses and peers and say, ‘Do you mind?’ ”