The University of Illinois at Urbana-Champaign has done a nice job summarizing the issues. These links provide further information from their scholarly communications website-
You choose WHO can publish your work and how it is disseminated.
Today, that means more than selecting the journals you’ve always published in or the ones your adviser recommends, it means researching and considering which publishers are going to meet YOUR needs. And besides publishing, you may want to think ahead to other dissemination models — such as an institutional repository — to help make your work as available as possible.
You control WHAT your publisher is allowed to do with your work.
The contract you make with your publisher determines what the publisher can do with your work AND what you can do with your work.
The Scholarly Publishing and Academic Resources Coalition (SPARC) is a great source of information on author's rights, including an addendum to standard publishing agreements. An Addendum is a legal instrument that modifies the publisher’s agreement and allows authors to keep key rights.
For Example: To secure sufficient rights to deposit the work in Digital Collections@TxState and to reuse their own work, the author could modify the language of the standard publishing agreement as follows:
“Notwithstanding the above language, I reserve the right to use this work in my teaching and research, for my colleagues at the Texas State University – San Marcos to use this work in their teaching and research, and I also reserve the right to place an electronic copy of this work on a publicly accessible web site.”
Bernard Becker Medical Library, Washington University School of Medicine, provides an informative list of phrases to look for in publisher copyright agreement forms. The document lists examples of rights and stipulations in various copyright agreement forms.
Here's a brief explanation of how your rights as an author may be impacted by publication