Keeping your chain clean and lubricated is one of the best ways to keep your bike riding smooth. The chain and sprockets on any bike are key to a smooth transfer of power from you (the engine) to the wheels (your propulsion system). Don't be stingy with the lube. Also, don't forget moving parts on the derailleur and brake mountings.
Keeping correct air pressure in your tires is the simplest, most important thing you can do to enhance your ride. You should check and fill before almost every ride. If you don't know the correct pressure for your tires, check with your local bike store.