There will never be a manual for the buckshot, but it’s no rocket-science either:

• Examine several services and communities for their relevance according your product or the compatibility of their users.
• Learn as much as possible about the offered features and tools and how to use them to your advantage, i.e the shout function on digg.com or broadcasts on blogcatalog.com .
• Create rooms, groups and further communities dealing with your topics and invite people who could be interested in your affairs. Share your knowledge and consider giving informations about your competitors (in a objective manner) and point out why your service/product is a better choice.
• Be honest, avoid vast exaggerations or desperately trying to hide weak points of your product. They be unvealed and this will be a backlash for and won’t increase your credibility.
• Use the feedback of the community, like emails, comments or blog reviews, learn from them and improve your product. Don’t forget to give credits back, so the critics might be teased and report in a positive manner about you.
• A community is a give and take – or at least it should be – so take part and comment, vote and pay attention to other users postings, they will reward it. Plus you will collect valuable information about your target audience.
• Keep your account up to date and fresh, nobody will interact with a nominal member.
• Do not act too aggressive, less is more sometimes. If you bother other users too much they will block you, mark you as spammer, kick you out of the community. Be sensitive, treat others like you would like to be treated. Messing it up, your good reputation and credibility will be annihilated and barely can be reestablished. So handle with care!
• Additional helping and useful informations that enrich the community related to your topic should be shared, too. This will integrate you as an active and worthy member and draw attention on your concerns. Only repeating marketing slogans like mantras is scaring and boring to people.
• Engage your friends, family, coworkers to join, vote for you or recommend your product and giving you an initial aid to start. Mostly a certain critical mass has to be reached after that the community gets aware of you and the rest is surfing the wave !

Good luck on your mission!