Hey,
the easiest way will be to create a new usergroup (groupadd newgroup) and put you into that group. Now you have to do
'chgrp newgroup /path/file' and 'chmod 770 /path/file'.
This should exclude other users to get access to the file.
Be careful. The file is not hidden from other users, because they have access to the folder. You have to do the same with the folder to avoid that.