Keep the drivetrain clean by lubricating with a penetrating lubricant, then wipe down the drivetrain, paying particular attention to the chain.

For the rest of the bike, unless you're riding in rain or mud, just a wipe down from time to time with a damp cloth or a bit of WD-40 sprayed on a cloth to get sticky stuff off. Keep any slippery stuff away from the brake pads or the sides of the rims. Use ammonia cleaner there, or a bit of vinegar.

Keep it simple.

EDIT: Penetrating lubricant, to me, DOES NOT mean penetrant, like Liquid Wrench or Kerosene, but rather a lubricant meant to flow into the chain's rollers. Just wanted to clarify...