As stated below, finidng a real estate agent that you are comfortable with and that you are confident in the abilities of is the key factor. A CMA ( Comparable Market Analysis) is the first step. Then if you are confident with your findings you can go with that information or you can have an appraisal done. The appraisal will be a cost to you but will give you good market value. This will allow you to make an educated offer or set an educated selling price.
As always this is general information.