You can just put a blank file named index.html in that directory.
A “more correct” way is to put a file named .htaccess in that directory consisting of only this line. Options -indexes What is especially nice about doing it this way all subdirectories of that directory also get their directory listings turned off.
You could then turn on indexes for one of those sub-directories. Just by making a .htaccess file in that directory with: Options +indexes