Provided you can find a rainbow, here are some tips for incorporating it into a good shot:
• Take the rest of the scenery into consideration. It’s exciting to have the chance to photograph a rainbow, but composing a shot that would even be great without it will make your picture twice as good.
• Help the rainbow stand out by positioning yourself so that it appears in front of a light background.
• Experiment with a polarizing filter to find different effects.