Well, if you have an always-on connection and a system running 24/7... then, read the appropriate man pages and configuration files, ensure OpenSSH is running, (I advice you to disallow root logins..) and permit only SSHv2.
If you can confirm the daemon is running, you'll need a way to easily address your computer... if you have a domain delegated to you it's an easy task, afraid.org can get you a free one. (And clients exist to monitor changes to your IP address..).
Finally, if you bpf/ipfw configured... allow connections to tcp port 22.