Listen to your chain, when it starts to chirp it's time to lube it. In rainy areas I would use an oil based lube so you don't have to lube it as often as you would with wax based lubes. The bummer is oil based lubes tend to attract dirtmore than wax based so you may want to use a rag to clean it prior to re-lubing. Just set the bike on a wall and pedal it backwards with one hand while holding a rag around the chain with the other. If the rag gets realy dirty, it's working! If you put the rag on the down side of the chain it doesn't "auto-shift" as easily.