Sharing data is a great way to increase the findability, accessibility, transparency, and integrity of research. First, you need to figure out whether your data can be shared. This means that you need to know your ethical and legal obligations (see the Plan page). If your data can be shared, there are a few choices to make about how you want to share your data.
Research data are considered a public good by many funding agencies in the US and internationally. They are putting in place policies to make data more openly available to the academic community and beyond. Sharing research data can have many positive effects (UK Data Archive).
If you are able to share your data, consider making it open data by choosing a CC0 (Creative Commons) license. You may also want to check out the Open Data Commons for data-specific licenses. A helpful overview of the differences is available from the Cornell RDMSG. Remember, factual data cannot be copyrighted, although specific database designs or presentations may be.