Well, what are you looking for:
Easy would be to pour some seawater on them and scrub a little. That will clean them up at least.
Harder (but not hard) would be to clean them with teak cleaner, then brighten with brightener and then oil. They will look nice but not for very long (unless you keep oiling them a lot)
Most difficult (not THAT hard and the best looking) would be to clean then with teak cleaner, then sand, and then varnish. Good varnish should last a few years.
Good luck,
Barry