As a warning, chain cleaning and lubing is often THE topic that results in very long running arguments on forums :P
My personal take is that chains are cheap enough that's it's only worth it to the bare minimum maintenance and swap them more often. That said, no need to buy a spare and alternate.
What I do is once a month I clean the chain quickly, on the bike, with a solution of simple green (dish soap would work as well) and a dollar store nylon brush. Dip the brush, press no chain, backpedal, repeat a few times. Then rinse thoroughly, wipe most of the water and let the rest dry a few hours.
Then I quickly apply TriFlow by resting the nozzle on the top of the chain and backpedalnig a few turns. Then some more pedaling to spread it around, and then wipe the excess. TriFlow is probably no the absolute best chain lube, but it works and I like keeping a big bottle around to use on everything, rather than a bunch of small, specialized lubes.
If I ride for a while in wet weather, I'll sometimes take 5 mins afterward to quickly wipe the chain of most grit and run a bit of oil. Fenders do help a lot in wet weather, not only for your chain but for your bottom bracket and headset bearings, and yourself! Consider getting a set if you don't have some already.
Whatever you do, the most important is checking for chain wear! Running a worn out chain for too long can dramatically accelerate wear on the rest of the driveline, which is a much more expensive fix. From
http://sheldonbrown.com/chains.html :
The standard way to measure chain wear is with a ruler or steel tape measure. This can be done without removing the chain from the bicycle. The normal technique is to measure a one-foot length, placing an inch mark of the ruler at the side of one link pin, then looking at the corresponding link pin 12 complete links away. On a new, unworn chain, this link pin will also line up exactly with an inch mark. With a worn chain, the link pin will be past the inch mark. [For accurate measurement, the chain should be held under some tension -- either on the bicycle, or hanging. Also, use a metal ruler or tape measure. Wood, plastic and cloth all can expand or shrink.-- John Allen]
This gives a direct measurement of the wear to the chain, and an indirect measurement of the wear to the sprockets. first, let's look at how to do this with a ruler that measures in inches.
If the link pin is less than 1/16" past the mark, all is well.
If the link pin is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
If the link pin is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
If the link pin is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.