Having houseguests during the holidays can be stressful. But keep in mind, BEING a houseguest during the holidays can be stressful as well! Here are my top tips for making them comfy this time of year.

Try spending a night in your guest room so you can experience it for yourself! You may discover issues you'd never know about otherwise. Get a fan if it gets stuffy. Try a noise machine if the garbage trucks are loud in the morning. Buy a rug pad if the bedside rug is super slippery.
Pack a cute basket full of travel toiletries and other items in case they've forgotten something.
Prevent awkwardness...have plenty of tissues, feminine products, matches, and toilet paper on hand so they never have to ask.
Provide a carafe of fresh water and a glass next to the bed. Nothing is worse than being thirsty in the middle of the night!
Keep some reading material in the guest bedroom. My own guest room just happens to house my entire bookcase, but you can always put a small stack of magazines, a short story collective, or a funny memoir on the nightstand. You want your guests to feel comfortable enough to be retire to their room if they need some space.
Leave the wifi password in an obvious place. I have a cute chalkboard in my office that I write a welcome message on along with the password. Bonus points if you write it on pretty paper and put it in a frame!
Provide an extra house key. Guests should never feel locked in (or out, for that matter).
Show them where things are for coffee and breakfast. Should they wake up before you, they should be able to help themselves.
One word: plunger. 'Nuff said.