You may not like this answer, but there is no one size fits all for metadata. The metadata that would best describe your data depends on the nature of your data. However, due to the fact that specialised systems for description (know as schemas) take time and expertise to implement, there are some generalised schemas that have been developed. These schemas include what are considered essential elements to describe any data.
Some disciplines have their own metadata schema. Each will have their own specified elements and structure:
|Astronomy||Astronomy Visualization Metadata (AVM)|
|Ecology||Ecological Metadata Language (EML)|
|Geographic||Content Standard for Digital Geospatial Metadata (CSDGM)|
|Social sciences||Data Documentation Initiative (DDI)|
Dublin Core is used by VU Special Collections and Archives.