Normally journal publishers will not accept work that is published or submitted elsewhere. Journal publishers in subjects where preprints are widely used will accept research that has been previously released as a preprint. As preprints emerge as a normal part of the publishing process in new subject areas, questions about whether preprints are regarded as previously published are still being worked through. It would be prudent to check the policies of journals who may be the ultimate destination of your research if you choose to publish your research as a preprint. You may also be required to agree to a licence when you deposit with a preprint server. You need to be sure that this won't conflict with possible journal publishers and won't restrict you future plans for your research.
Journal publishers encourage the publication of preprints after a paper has been accepted. This is the Green Route to Open Access publication. Publisher’s policies on preprints after publication / submission can be checked on the SherpaRoMEO database.