Exercise is a cure for many things, including poor sleep. Take a brisk walk in the afternoon. 20-30 minutes is fine. It's not guaranteed, I guess, but it always works for me.

Also, if you're a coffee, tea or soda drinker, switch off to herbal tea or plain water after lunch. Caffeine has a 6-8 hour period of effect, with the peak effect happening at about the 4 hour mark. If you do drink things with caffeine, consider reducing or cutting them out entirely. I can drink 2-3 cups of green tea in moderation without any adverse effects, but more than one cup of black tea is too much (and one isn't quite enough, so I don't drink black tea). Coffee and sodas aren't worth it, to me, as the caffeine in coffee is a jittery spike and all the sugar in sodas makes me sleepy by lunch time (which totally throws off getting to sleep when I actually want to at night).