A really simple and time-tested device is called 'word painting'. Here the composer uses pitch to outline the meaning of the words. A brilliant example is used by Handel in 'Messiah' in which he rises up on 'every valley shall be exalted' and then dives down the scale in the line, 'every mountain and hill made low'.
I used this technique when setting the tune to 'Under the Leaves' and came up with a tune that works really well.