For that you’ll need to do the following:

1 Don’t support older protocols. A lot of servers support really old and obsolete protocols. If you run a web app, your users will very likely not need support for these.
2 Don’t support flawed SSL ciphers. There’s a bunch of these and you can avoid using them. Browsers support multiple different ciphers, so this is not a problem.
3 Cache SSL sessions. This will improve performance.
4 Turn on HTTP Strict Transport Security (HSTS). This is a special header that will tell browsers to never connect to the server via normal HTTP.

server {
  # deferred allows for faster connections if there's
  # no other servers on port 443 defined
  listen 443 ssl spdy deferred;

  ssl on;
  ssl_certificate /etc/nginx/your-certificate.crt;
  ssl_certificate_key /etc/nginx/your-private-key.key;

  ssl_prefer_server_ciphers on;
  ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
  ssl_session_cache shared:SSL:10m;
  ssl_session_timeout 10m;
  ssl_stapling on;

  # tell any upstream things like unicorns that we're on https
  proxy_set_header X-Forwarded-Proto 'https';
  underscores_in_headers on;

  location / {
    add_header Strict-Transport-Security "max-age=31536000; includeSubdomains";
    # ...

  # ...