These are the correct file permissions for WordPress:

chown www-data:www-data -R *
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;
chown username:username -R *
chown www-data:www-data wp-content

Whilst this configures the appropriate file permissions and ownership for a WordPress installation it is recommended to carry out additional hardening of security of a WordPress installation.