1. You get the blogger's name wrong. No one will take your email seriously if you misspelled their name.
2. You send a generic email blast. This is especially bad if you happen to CC all the other blogger's addresses for everyone to see. If you're going to do this, at least do a BCC (blind carbon copy, which means that no one other than you can see the addresses).
3. You place them on your mailing list without advising them first. Most email service providers prohibit this anyway, as they want everyone on your lists to voluntarily opt in. Music bloggers particularly hate this though, so don't do it unless they ask.
4. You turn on the SPAM machine. Music bloggers hate when you keep badgering them with the same info. It's OK to follow up or send a reminder, but if they don't respond after a couple of tries the chances are low that they're going to respond at all.
5. You don't read their blog before emailing. Bloggers hate it when you send them something that blatantly indicates that you've never seen their blog before. It's the ultimate turn-off, and will probably get you permanently banned from the site.
Want to know the way to a music bloggers heart? It's simple really. Contribute to their blog with regular comments that are not self-serving in the least. When you become a part of their community, you're much more likely to get a blogger's attention when you need it.