Which MetaData Fields I Fill Out to Describe My Photos?

MetaData is an information about the picture carried with the digital picture in the same file (e.g. picture.jpg). There are more standards of MetaData (XMP, IPCT, and others)
Unfortunately there are not the only one title for various fields used in MetaData. I write all I know separated by slash. 
So now what I really need and because of compatibility between different software I use: 

• Headline - just headline
  
• Object Name/Title - the same as above
  
• Caption/Description - one sentence or paragraph describing the picture
  
• Keywords/Tags - probably the most important part, later I can search through my pictures and catalog them
  
• Byline/Creators/Author - author of the picture
  
• Copyright - copyrights...
  
• Contact - multiple fields value, like e-mail, WWW, tel., etc.
  
• City and Country - where the picture were shoot
  

The others fields I'm leaving empty for now.
I use XnView or Photo Info to fill the MetaData out.