Right from the LinkedIn horse’s mouth:
Focus on quality: When it comes to your professional network, the quality of your connections is more important than quantity. Connect with people you’ve done business with, who can vouch for you, and who you’d feel comfortable vouching for yourself.
Personalize your invites: Customize your invitations…Writing a personal note goes a long way in strengthening the relationships that make up your network.
Please adhere to these suggestions; no more blind connection requests-it’s not just me saying this; it’s LinkedIn too. (From the description of the newly-enhanced People You may Know feature.)