How to Link

HTML

Use the Link button

Make it obvious where the link leads

Contrast

Encourage flight?

Sidebar

What to Link

External links

Related content

What is the reward for following the link?

Internal links

What not to Link

Punctuation marks

Headlines

Why to Link

Credibility

Site traffic

Interactivity

1) Provide context for your article 2) Provide attribution 3) Reward readers with something extra or another layer or dimension to the story

References

http://webdesign.about.com/od/beginningtutorials/qt/external-links.htm