Values for modified Browser Caching

This strongly depends on what you are doing with you´r website. If you´re developing on the html, css, js files… I would suggest you to wait until you finished and then set the values to 1 month. If you make changes in those files and set the Expires to a long time, you´re users won´t see those changes until the chosen time span ends. Or for example if you definitly know that you will not make any changes on specific files (e.g. JavaScript), you can set the Expires for those files to a very high value.