Below you will find some essential hints which you should keep in mind at all times to avoid mistakes most commonly made by beginners and live longer, with some luck on your side. Of course practice is the most important thing.
Don't get too attached to your character's life. Before you really start playing, it's best to train a bit. Play hide and seek with the Zeds to learn their behaviour schemes. Learn from how high you can jump without breaking your leg or ending up shocked. Check out what you can find in various places on the map. Just do whatever comes to your mind. You don't lose anything when starting from scratch and you can earn some precious experience.
Get used to crouching and slowly moving through areas other than vast fields and thick woods. Each careless move or noise can draw the Zeds attention.
Moving while prone (with [SHIFT] held down), you become almost invisible to zombies. Of course keep safe distance at all times.
Shoot Zeds only as a last resort. The noise will draw in even more of them (not to mention giving away your position to other players).
Because of weak synchronization, zombies can still be running a while after you shoot them. Wait a bit before shooting again and make sure whether the last one was deadly or not.
In case of being chased, head to the woods or find shelter in open buildings. You can lose zombies easier in the woods, while buildings make Zeds to slow down and in effect they can lose track of you.
Even shallow water can stop the zombies for long enough for you to be able to outrun them to a safe distance.
Don't swim for too long, or you might lose some of your items and lower your temperature.
You can easily draw the Zeds' attention by throwing something at them. It especially applies to flares and smoke grenades, as they're attracted to the sound they make. It can buy you some precious time to escape.
Play on servers which are during daylight. Remember that you can always change server to one with the sun still up.
When shooting, switch to first person perspective and use the optics in your weapon by pressing [PPM]. Better accuracy is fewer bullets used and less sound made.
The more powerful your weapon is, the louder. Remember about it when shooting in the city, where there are lots of Zeds and other players.
Only buildings with open doors or interior visible through windows are accessible for the player. Others are just props.
The most precious items can be found in military bases, supermarkets, churches and Deer Stands.
Make sure to always have food, drinks and medicine with you. You can survive even without any weapons, but not when your bleed to death or can't walk because of a fracture.
Don't kill other players without a reason, unless you feel threatened by them. Carelessly killing everyone, you promote such behaviour and might miss a chance to fight alongside someone.
If you have an advantage over another player (you're hidden or better armed), ask if he's friendly and carefully investigate (however remember about the below point).
DON'T TRUST ANYONE, unless he earns your trust by, for example, helping you in need. Nevertheless, be careful even then, to avoid becoming a victim in the least expected moment.
Avoid groups of people, especially if they seem to be members of a clan and are well equipped. Clans don't usually recruit random people and treat them as walking supermarkets instead.
Notorious murderers can be recognized from other survivors. If you can hear a heartbeat after looking at another player, you have two options: if you can, kill him first, if not, RUN (at best silently).
If you kill a bandit, don't approach his body immediately. Such people often walk in groups. Check his corpse after making sure the area is safe, take what you need and run away.
You want to avoid confronting other players? Choose the least populated servers.
PvP is an integral part of the game. Don't get mad if someone kills you and don't hesitate to kill others, if there's a need to.
Be patient. DayZ requires experience and nerves of steel. Hasty decisions ill-considered choices can only cause your trouble. DayZ is in fact closer to games like Thief than Call of Duty.
Don't spend more time than needed in the city. Collect resources and run to the woods. Each moment spent in the city can end up in dying, especially from hands of other players.
Spots containing loot can be easily identified. If something looks like a pile of empty cans, it most likely is nothing more than that and you won't find ammunition between them. Don't waste time on looking through garbage.
Explore Chernarus. The cities and villages at the south coast serve only as warm-up before the real adventure.
A very good time (in game) to search for loot is the time between 8 and 10 p.m. It's rather dark then and you're much less visible, while you still shouldn't have problems with moving freely. The same applies to time between 3 and 4 a.m.
Check for updates to ArmA 2 and DayZ daily. Patches tend to come out almost each day.
Never give up. Death in DayZ is unavoidable. Sometimes it comes from unwariness, sometimes from pure accident/bad luck or bugs in the game. Keep that in mind and learn to start from the beginning.
Sometimes, retrieving that you've lost might take just a couple minutes. Everything depends on luck and your experience.
Each death brings new opportunities. With time, you will understand that starting from the beginning is most exciting.
DayZ isn't easy or fair and every second players is a rotten apple. Having all that in mind, play, experiment, explore and approach the game normally.