Setting up NGNIX to redirect from non-www to www

Can anyone help me set-up the non- www to www redirection?

I 've tried Several tutorials here and not works, my nginx is:

server { listen 80;

server_name mydomain.com;

location / {
    proxy_pass MY_IP_SERVER:8080;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
}

}