The following are things to bear in mind, rather than hard-and-fast rules:
Introduce yourself. It’s important that followers know who the contributor is for that week, so take the time to introduce yourself. It might be a good idea to post a link to your Biotweeps introductory blog post at the start of each day.
Make it accessible. Biotweeps iss a general science communiction project with a audience comprised of a wide variety of people from all walks of life, including biological science academics, to naturalists, to experts from other fields, to those with a general interest in science.
Keep it short. Sometimes it is necessary to use multiple tweets to explain something. However, remember that followers will not necessarily see the entire stream so try to keep your tweets self-contained wherever possible.
Engage in conversation. Respond to people who interact with @biotweeps.
Credit creators. If you post a link to an article, picture, etc., @mention the creator or source.
Use hashtags. Hashtags, e.g. #biotweeps, are used by Twitter to categorise tweets. Many events and discussions have associated hashtags. Using them increases your exposure and potential for interaction.