Don't overstay your welcome
Once the fling has been flung, get out. Waking up together is very "couple-y," and curling up next to warm body can breed attachment. That doesn't mean you need to bolt for the door (or kick him out) as soon as the deed is done. A few minutes of conversation followed by a "Thanks for coming over," or an "I really should get home," sends the message with minimal drama. Sometimes, though, sleep happens. Whether there was enough chemistry to seduce you into basking in the afterglow or whether alcohol made it impossible or impractical to hit the road, you've now got to get out of there in the light of day. Best-case scenario: Both parties are clear in advance that the encounter will only be for one night, and you part ways with a simple, "That was fun. Take care." Unfortunately, the combination of alcohol and hormones may mean that you skipped the first step (clarifying expectations), and you could roll over, open your eyes and say to yourself, "Oh, my God. What did I do?" or worse, "Who the hell is this?"
Sneaking out is not an option. If you are gutsy enough to go to someone's home in the middle of the night, be gutsy enough to let them know you're leaving. If you two stumbled back to your place, making a break for it is clearly out. Getting up and getting dressed, however, is perfectly acceptable. If you've got a snoring lump who doesn't wake up when you're opening dresser drawers and turning on the faucet, a gentle tap on the shoulder accompanied by, "Hey... I'm sorry to wake you, but I need to start my day," should do the trick.
Pick up after yourself
If you're on the receiving end of such a farewell, be friendly, don't dawdle and don't even think of "accidentally" leaving your watch/bra/cell phone. It's obvious. It's annoying. And it looks desperate.
Thank your host
Of course, it's possible that you sincerely enjoyed the company of your late-night lover, and that you think he enjoyed yours, too. Pay attention to nuance here: there are lines between interested and polite, and politely uncomfortable and sprinting for the door. Unfortunately, the lines can be faint. If you roll over to a smiling face and you're game for another go-round, by all means, take a tumble then go for eggs and see what happens. Or go with the ever-direct, "You know, I enjoyed your company. I wouldn't mind seeing you again." If he bites, he'll get your digits. If he looks shifty and uncomfortable, there's no point in back-pedaling. You know where you stand.
If he's the one in hot pursuit but you just wanted a fun fling, simply say, "I had a great time, but I'm not looking to date right now." Don't waiver, but don't be a jerk about it. Thank him for coming over, and hug him good-bye at the door. Being polite and respectful keeps everyone's dignity in tact. And politeness and dignity are what manners are all about.