In order for us to fall asleep, we all need to accrue a “sleep debt,” which lets us feel tired and ready for bed.  Napping cuts into that sleep debt and leads to difficulties falling asleep, or sleeping in increasingly disjointed chunks.  To keep your sleep schedule more regular, and your sleep more restful, it’s better to avoid napping at all and instead let yourself be a little more tired going into the evening.  Worst case, if you simply must take a nap, try to keep it brief and before the early evening.  A better alternative might be taking a brief walk outside, doing some stretching, or spending a few minutes on an enjoyable task (like playing a game) before returning to your to-do list.