Improving the quality of your sleep doesn't necessarily mean sleeping for longer. In fact, sleeping in on the weekends will throw your natural rhythm out of sync, making it harder for you to revert to a normal pattern in the following days. Six hours' shuteye is generally considered the minimum for optimal functioning during waking hours but it's important that they're six truly restorative hours.
Avoid nightcaps or midnight snacking, as raising your blood sugar level before bedtime will have a negative effect on the quality of your sleep. A quick drink may help you 'nod off' but it will prevent you from going into a deep sleep. And without REM sleep - the truly restorative kind - you'll look and feel less refreshed in the morning.