Transfering Copyright vs. Granting a License
It is preferable to keep your copyright on an article, but a number of journals, especially from commercial publishers, require that you transfer the copyright to them. If you do transfer your copyright, look for language about the rights the journal licenses back to you, especially the ability to re-use your work in other publications. Actively negotiating for the right to publicly post your article, or at least a pre-publication version of your article, is the best way to increase its visibility.
Permissions to Post Your Article Elsewhere
Even if you keep your copyright, you will likely be granting the publisher a license to disseminate the work in various formats. Be cognizant of contract terms granting an exclusive license.
However you structure your agreement, it is a good idea to have specific language about what can be posted to an institutional repository, and what can be posted to SSRN, and when it can be posted.
For further help, please contact Craig Eastland (c.eastland (at) northeastern.edu).