Straight from the minecraft wiki http://minecraft.gamepedia.com/Tutorials/Beginner's_guide
As Minecraft is a sandbox game, there is no defined or proper way and style to play the game. However, one common theme found throughout gameplay is the need to feed yourself, and to avoid (and later, fight) hostile mobs that spawn either in dark places (e.g. caves) or when night falls.
As your first day begins, you will need to collect wood. Use this to make a crafting table and a wooden pickaxe. Then dig a small stairway into the ground to collect at least 29 cobblestone for a full set of stone tools, and a furnace. You then want to make a shelter (dirt or wooden shack), or if available, stay in a village. After that put down your crafting table and furnace and smelt some wood into charcoal, and make some torches with that.
For nighttime, the primary danger will be monsters. It is a good idea to stay in your lit shelter. If you don’t have armor and a sword, do not try to engage any monsters! The worst way to die early on is to be killed while trying to hunt monsters, so don’t do it!
Normally in survival mode Minecraft, when you die, all items you were carrying or wearing in your inventory are scattered around your point of death while you respawn elsewhere. Until you sleep in a bed, you will spawn somewhere within 10 blocks of the world spawn point. This includes the first time when you started the game, so you can respawn anywhere within 20 blocks of where you first entered the world.
The traditional advice is to build your first shelter as close as possible to the spawn point, so if you die, you can easily find it again, or even spawn in a now-protected area. Even with the variation in where you’ll come back, it’s good to have a lit shelter nearby the spawn point. However, a problem with sheltering away from spawn is that if your death site is too far from where you respawn, your items may despawn while you’re trying reach them. (See below for more details.)
Like any dropped items in Minecraft, the items you drop when you die will despawn (disappear) after 5 minutes, unless you’re more than 180 blocks or so away, that is outside of chunk update radius The problem is that if you died at night, you will find yourself stranded without your weapons and armor, so you are quite likely to get killed again, or at least find your stuff guarded by monsters. Meanwhile, some of the monsters can actually pick up your stuff and use it against you! And if you spawned near your death scene, that 5-minute timer can easily go by before you can actually get back to and keep your stuff.
However, the above only applies until you have made and used a bed in a secure shelter. Once you’ve done that, you have a new option: If you get killed at night, you will respawn next to your bed, so you can just go back to sleep, and wake up the next morning — the items don’t “expire” while you’re asleep. It still may be worth keeping your bed out of chunk update range from where you’re endangering yourself, but at least you won’t be stranded outside at night.
Food and hunger
Once you have tools and shelter, your next priority will be food. Hunger will take a while to hit, so it shouldn’t be a problem on your first day, but you’ll try to pick up some food for when it does. However, after you’ve been moving around for a while, your food bar will begin rippling and start to decrease. If your food bar drops below 90%, you will not regenerate health, and if it gets to 30%, you can’t sprint. If the hunger bar goes down to empty, you will begin losing health. Unless you’re in Hard mode (and a beginning player shouldn’t be), you can’t actually starve to death, but you will go down to 1 health point (Half Heart.svg) in Normal mode or half your health (Heart.svgHeart.svgHeart.svgHeart.svgHeart.svg) in Easy mode, and that leaves you quite vulnerable.
Walking, mining blocks, and even placing blocks all cost some hunger, but all of those are minimal compared to the items below. These are the things that cause the most hunger, in order of cost.
Healing damage of any sort. Avoid taking falls of more than 3 blocks, drowning yourself, or otherwise taking damage, as healing damage costs a lot of hunger. Especially avoid…
Fighting: Both attacking mobs and receiving damage cost hunger, even before you start trying to heal damage. (10 blows either way matches healing Half Heart.svg, one health point.) You will need to slaughter a few animals, but pick your fights carefully.
Sprinting. If you double-tap the forward movement key (W by default), or hold your sprint key in (Left Ctrl by default), you will sprint. This moves somewhat faster, but it also uses a lot of food, especially if you go any distance. (30 meters matches healing Half Heart.svg.)
Jumping. Obviously, you’ll need to jump some just to get around, but don’t bounce around randomly or unnecessarily. (15 jumps matches healing Half Heart.svg) Sprinting jumps are especially costly, 4 times as much as a regular jump, although they are the fastest mode of transportation early in the game.
Note that if you’re (staying) at full health, and not moving, fighting, mining or placing blocks, then you will use no food. Thus if your character has a secure place to stay, you can just stay put to conserve food while waiting out the night, a storm, or crop/animal growth.