Basic topics and top 10 ways to use Twitter described in more detail here:
http://www.socialedge.org/blogs/the-edge/archive/2009/05/04/twitter-and-the-social-entrepreneur

Don't use Twitter just for marketing or Pr - align with your organization objectives. Make it part of your programs, and let whole organization leverage it (rather than silo'd approach).

Keys are listening and learning and discovering key influencers and information in your field.
Overview: 10 ways to use twitter:
Networking
Knowledge
Research
Educating
Increasing Awareness
Filtering
Events/conference converage
Fundraising
Announcements
Friendraising

Tips and Tools:
finding people and subjects (search by keyword, hashtag, or name) search.twitter.com twitterfall.com tweepsearch.com mrtweet.com
understanding your twitter community quantify growth: twittercounter.com tag cloud from followers bios: twittersheep.com
mapping your followers: pipes.yahoo.com/mmmeeja/twitterfriends tweemap.com
tracking and url shorteners - http://bit.ly
alerts monittor.com and tweetbeep.com
clustering on issues besides hashtags - twitter groups and twibes.com (there is a twibes.com/socialentrepreneurship)

Also talked about:

• having two twitter accounts - personal and professional - the latter being mission focused, yet still personal
• who to follow - still unclear - reciprocal nature =follow everyone who follows you versus selective - provide a filter for others seeking info on who to follow in your field can look at your very selective list.
• having the CEO twitter - often people will have more followers than orgs esp if it is the CEO - people like having a direct channel to leadership
• twitter has a timely component - being the first to share information, sharing deadlines, etc.
• twitter has a perishability - comments are generally gone within 24 hours. If you retweet - wait ~8 hours, try to include an update or additional info
• twitter content should not be vague - Please no "I've updated my blog" comments (that's what RSS is for) - instead choose a key learning or message from the new post and then link to the post (saying it is new doesn't help anyone, and really is a given on Twitter)
• listening on Twitter can result in responding to reporter inquiries and getting mentioned in articles (reporters using Twitter for quick research)
• Zappos uses Twitter well and rewards staff NOT on the sale but on the lifetime value of the customer - so quick responses, resolving issues even if there are returns adds to lifetime value. Community and twitter relationship can add to lifetime value of a donor.

Mashable was recommended for lists on how to Twitter (and how not to Twitter)