Most grunt modules that work with files have a ​files​ property where you can set which files it would act upon:

      dev: {
      files: {
        'dist/index.html': 'src/index.html',
        'dist/contact.html': 'src/contact.html'
      }
    }

If you want to be able to process any file in any directory you can use this format:

      dev: {
      files: [{
         expand: true,
         cwd: 'src',
         src: '**/*.html',
         dest: 'dist/'
      }]
    }

The code above processes all the pages placed in the “src” directory and its subfolders.

  // Minifies html
module.exports = {
    dist: {
        options: {
            removeComments: true,
            collapseWhitespace: true,
            minifyCSS: true
        },
        files: [{
            expand: true,
            cwd: '<%= paths.dist %>',
            src: '**/*.html',
            dest: '<%= paths.dist %>/'
        }]
    }
};

Source: http://www.sitepoint.com/5-grunt-tasks-improve-performance-website/