In addition to lubing the obvious external parts (chain, derailleurs) remember that your bearings (hubs, bottom bracket, headset) need extra care if you ride in the rain very much. Make sure you get them repacked at least once per year, and preferrably twice, if you do alot of wet riding (unless you have sealed bearings of course). A good syn grease will stay in place a long time, but not as long in wet conditions. If you take the bike to a shop for an overhaul, be very specific that you want all your bearings repacked. Then take the bike home and feel what a well lubed hub, BB, and headset feel like (remove the wheels to feel the hubs). When they don't feel like that anymore, it's time for another relube.