1. Be relevant. 2. Be personal. 3. Be clear. 4. Show what's in it for them. 5. Be appreciative.

Also, provide them their talking points. Creating the narrative for them increases the likelihood of them blogging about it in the first place. On the other hand, if you do not, and they decide to blog about it, the narrative they write may not be what you were looking for, and could even be negative.