Trust-factor within the network: Social sites like LinkedIn are not only about networking but also deal with trust. It is possible to send mails to people outside your contact(one / two at a time). Your friends, however allow you to send them mails because they trust you. So, always send some value-added mail to them so that they do not feel betrayed.
Show modifications on "update status" rather than "emails": People generally prefer looking at updates (blog posts, events, profile settings etc.) to know about the recent changes inculcated by their friends. Sending email states urgency and sending promotional links to your friends would count you as a marketer and they can block you from their friend's list.
Participate smartly in group discussions: After joining related groups, do not post link of your targeted site abruptly. Start with some meaningful posts that would help others. Create groups to encourage sharing of market-intelligence and increases your web presence.
Give & receive recommendations: We generally read reviews of a movie before watching it. Similarly, people tend to see your past client's experiences before they accept your services. So, ask your friends and trusted companies to give you good recommendations so that people are interested in your services. Give recommendations to your friends too.
Enable feeds for network updates: LinkedIn provides network updates feed that publishes your personal Network updates in
RSS format to help you know about your friend's new connections or latest news.