Get enough sleep
I have a theory about sleep. My theory is this: everyone who routinely uses an alarm clock suffers from chronic sleep deprivation. Using an alarm clock a few times a year (to catch a plane or have a phone call with someone in another time zone) is fine. But routinely getting up before you wake up naturally is sleep deprivation, no matter how much it has become normal in today's world.
There's lots of evidence that sleep deprivation is bad for you. It weakens the immune system. It probably causes both cancer and type-2 diabetes. It almost certainly reduces the survival rates for people who have cancer. It raises blood pressure and probably causes cardiovascular disease. It's associated with all manner of health issues from headaches to hernias.
There's really no doubt about the harmful effects of severe sleep deprivation. Its use as a torture technique has led to a significant body of study. It's quite straightforward to induce psychosis with just a few days of sleep deprivation.
It is the effects of mild sleep deprivation--the sort experienced by most people in the developed world, where waking up with an alarm clock is part of normal life--where there has been some debate. But even there, the evidence is that routine sleep deprivation is bad for you, even if it's mild.
Every year there's an unintentional experiment on the effects of mild sleep deprivation: The spring beginning of daylight savings time, where everyone's weekend is one hour shorter than usual. The following Monday there is a significant increase in traffic accidents.
A really interesting 1995 study of researchers who spent a summer above the arctic circle found that the amount of time they chose to sleep (when there were no external cues from daylight or timepieces) was 10.3 hours per day. That's probably closer to what's normal for humans than the 8 hours that is considered standard or the 7 to 7.5 hours that most Americans actually get.
The internet is full of advice on dealing with sleep deprivation and with sleep disruptions caused by such things as shift work. Ignore it. Coming up with tips and tricks to deal with sleep deprivation is as crazy as coming up with tips and tricks for dealing with putting arsenic in your food. The answer in both cases is simple: don't do that.
If your employment or schooling depends on early rising, go to bed early. In particular, go to bed early enough that you do not need an alarm clock to wake you. If circumstances in your life make that impractical, either change circumstances or change your employer or school. The only good reason to tolerate chronic sleep deprivation is to rear an infant--and then only for the necessary few months, and preferable with the sleep disruptions divided among at least two adults.
If you can't get enough sleep at night, take naps. If you're getting almost enough sleep, a short 20-minute nap can make up the difference. On the other hand, if you're getting less than 8 hours of sleep, you probably need more than a short nap. A nap that lasts a full sleep cycle--long enough to go into deep sleep and then come out of it naturally--will actually provide some of the sleep missed during the night. Like everything else about people, sleep cycles vary from person to person and vary from time to time for one individual, but 90 minutes is a good first guess.
I have enormous sympathy for people who suffer from sleep disorders. If the problems that keep you from getting enough sleep are not external social pressures, but rather are internal physical or mental issues, do whatever it takes to get the problem addressed. Start with your physician or visit a sleep clinic. Basically, if your sleeping life is a shambles, your waking life will be a shambles as well.
I've talked before about how important for being happy it is to find the right work--work that helps people or produces something of value, work that uses your talents and is respected by your peers. Finding the right work is probably the second most important thing in determining whether you're happy or not.
The most important thing is getting enough sleep.