If you've ever sent a request to connect on Linkedin, choosing the 'friend' option ... and you don't know the person in the slightest, this blog post if for you. Linkedin is NOT Twitter. It's a professional business network with certain barriers in place that make it more challenging to connect with people. And that's a good thing.
It's not a contest to connect with the most people. It's a place to connect or re-connect with people you've met (in person or online), worked with or worked for, in some form or fashion. It can also be that place you first meet someone, via groups, Inmails and such. But if your first instinct is to fire off a bunch of connection requests the easy way, via the 'friend' option, your first instict is wrong. Do a little homework, locate the person's e-mail address, choose 'other', and insert e-mail. And then - this is key - tailor an introductory message so it's not the pre-populated, impersonal form note.
There are no second chances to make great first impressions.