I use this post all the time and figured I should make another copy of it so that I can find it faster.
Use these commands to fix your permissions on your WordPress site.
chown www-data:www-data -R * # Let Apache be owner
find . -type d -exec chmod 755 {} \; # Change directory permissions rwxr-xr-x
find . -type f -exec chmod 644 {} \; # Change file permissions rw-r--r--