Configure your instance using this guide to install the necessary packages and setup VNC to start on reboot.
Tip: You will want to connect via SSH tunnel to your VNC server. That is the safest way to do it.
Specify the resolution using this format
vncserver :1 -geometry 1600x1200
Credit: https://stackoverflow.com/questions/15816/changing-the-resolution-of-a-vnc-session-in-linux#1083668