First, you should experiment with Twitter before starting to use it in a real marketing campaign. Also, I don't see truly SEO advantages using Twitter, instead it can provide benefits on your marketing activities.

Here's some tips.

1. Use Hashtags
2. Don't forget to use keywords in your messages
3. Don't abuse with posting links to your website
4. Be polite

Twitter is a good social network, I think that is possible use twitter for a service company (like web agency, or similar) that in speed mode and with simplicity communicate with other :) and is a good thing for Search Engine that like a fresh content ;)