By default apache is configured to show following files instead of directory listing:

DirectoryIndex index.html index.cgi index.pl index.php index.xhtml index.htm

You can recursively list all these with this:

find /var/www -name 'index.*'

If your directory have any of those, apache will show it, instead of something like this:

To fix that, delete or rename index.* files to something else. Alternatively, you can change DirectoryIndex directive and reload apache (/etc/init.d/apache2 reload).

By default, apache DocumentRoot is /var/www. Only files under that folder are displayed. Additionally, symlinks are followed only if destination is owned by same user. If you have files under /var/www, you don't have to care about that.

Apache does not list files that www-data user can not read. As long as there's r and x the last group (marked with ^ below), everything is fine:

drwxrwxr-x  4 user group     4014 Feb  4 23:16 filename

       ^ ^

Technically, you only need x for folders. Your commands for changing the permissions were correct:

chmod -R 755 /var/www  

If apache does not list any files even if you don't have any index files on your folder, use

tail -f /var/log/apache2/error.log

to see which errors apache encountered.