Today's tip ... okay, this is good whether you dabble in watercolors or your are proficient at it.
I highly recommend getting yourself a box of Strathmore Watercolor Cards. They come in a box of 10 or even a box of 100. They're made of 140 lb. watercolor paper and have a matching envelope with a pretty deckled edge. They do have an unusual sizing, not quite the same as painting on regular 140 lb. watercolor paper. I like to paint on the rougher side.
They are perfect for doing a quick little painting that doesn't involve using a lot of water or a complete background wash. More paint, less water and a medium sized round brush is perfect to whip up a quick card anytime you need one for any occassion.
Save a trip to the card shop and create your own. Your friends and family will love you for it!