Hacker's A Writer's Reference, 8th edition [Roanoke College edition] pages 386-9 has this to say about Annotated bibliographies.
"Once you have created a working bibliography, you can annotate it. Writing several brief sentences summarizing key points of a source will help you identify how it relates to your research argument and to your other sources. You should evaluate the source in your own words and use quotations sparingly. Clarifying the source's ideas at this stage will help you separate them from your own and avoid plagiarizing them later."
Marginal hints are:
- Annotations should be three to seven sentences long.
- Use quotations sparingly. Put quotation marks around any words from the source.
- Interpret the relationship between this source and others in the bibliography.
- Evaluate the source for bias and relevance.
See the Sample Annotated Bibliography Entry page 387. You can find a copy of Hacker's A Writer's Reference at the Reference Desk, main floor of the library; just ask the person at the Desk.