First do a quick scan of the hardware physically (look for keylogger hardware on the keyboard plug/cable). For the truly paranoid, bring your own keyboard. (as keylogging modifications may be present inside the keyboard.)
Boot into your own pre-prepared OS from usb stick or cd. (prevents any malware or spyware already present on the machine from affecting you). An OS on read-only media might be more secure.
Even after all that, you still can't trust the machine as it is still possible for rootkits to be present.
At that point you can start an ssh or vpn connection to your home machine/network, and work remotely. Just be aware that any key negotiation may be intercepted by a man in the middle attack. You can put your ssh key on the read-only media along with the os.
You can never really truly trust interacting with a public machine in the end, no matter what measures you take.
Always be aware of the possibilities of the hardware logging your keystrokes, man in the middle attackers on the network, etc...
As is usually the case when it comes to security, you provide layer upon layer of protection, and hope that your layers are thicker than the determination and ingenuity of any potential attacker to compromise you.
You can either go very far with all this, or decide that a simple ssh tunnel with your keys on a usb stick is sufficient. There will always be risk, and how far you are willing to go to diminish that risk is up to you in the end.
(Personally I wouldn't touch a public computer to do anything important with a ten foot pole, no matter what measures I think I have in place.)