Try this guide. Some templates here:
http://www.seomoz.org/blog/broken-link-building-guide-from-noob-to-novice
Customize and tailor each email as much as possible. Really look at the target site, follow them on twitter, learn about them, etc
For example, I recently started following a target. I was going to do a broken link email, but soon enough, they were ranting in a blog post about their brand usernames being taken by squatters and inactive accounts on twitter/facebook. I used that to reach out to them and suggest what to do to claim their usernames since I actually had the same problem. I didn't even mention or request links, but they are now linking to our homepage and referencing other pages on my site. All I did was sign my emails with my domain name, so they know who i am, where i'm from.
Essentially I made a friend by offering value, and asking for nothing in exchange. That target would have been tough to get a link from otherwise.
In case that hadn't worked out, I WOULD have eventually asked directly for the link after having made a great first impression.