There are a plenty of improvements that can be made according to ssllabs.
First you should generate your own DH-Parameter
openssl dhparam -out dhparam4096.pem 4096
and then use them in your nginx config file
ssl_dhparam /etc/nginx/dhparam4096.pem;
Disable TLS 1.0:
ssl_protocols TLSv1.1 TLSv1.2;
Enable session caching:
ssl_session_cache shared:ssl_session_cache:10m;
Disable weak cipher:
ssl_ciphers ECDHE-RSA-AES256-GCM-SHA512:DHE-RSA-AES256-GCM-SHA512:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384;
For a complete list, see https://cipherli.st/