I've stayed alive for 109 days in Minecraft by doing the following:

• Carry a diamond sword.

• Carry a bow with a full stack plus a working stack of arrows.

• Wear iron armor with never more than three notches gone off it.

• Keep full or nearly full hearts, and always carry at least two pork chops.

• Look where you're going to land when you jump.

• Never fall more than three meters.

• Do not ride waterfalls into unknown territory.

• Never dig straight down or hold forward as you dig out the block in front of you.

• Don't go into unknown territory without a way back out.

• Always carry plenty of torches as well as extra coal and wood.

• Crouch near edges.

• Don't go near open lava more than necessary.

• Shoot creepers, skeletons, and most spiders with your bow.

• Don't work on ledges at dawn or dusk when computer usage spikes due to lighting updates.

• Don't dig straight up, and don't panic when gravel, sand or lava comes at you from above.

• When tunneling to the surface, be prepared to duck back in your hole if it's dark, or if you're under ice.

• Don't wander around outside after dark.

• Eliminate night as much as possible by sleeping.

• Sleep at the earliest possible moment, especially when near forests.

• Sleep with sword in hand, and make sure your bed is secure.

• Make multiple exits from your base, with glass exit rooms so you can see around the door.

• Carry a bucket of water and a stack of cobblestone in belt slots.

• Remap your drop item button.

• To eliminate a heavy monster infestation, travel far away and then come back.

• Create closed off dark areas or a mob tower where most monsters can spawn harmlessly.

• Don't use more than a single TNT block at a time, and get at least fifteen blocks from it.

• Don't go away from your keyboard unless you're 100% secure.

• When digging gravel or sand, avoid standing on gravel or sand that's connected, unless you've already dug in the area.

• Add fences to ledges in heavily traveled areas.

• Don't build with wood anywhere near fire or especially lava.

• When exploring near heights or lava, kill everything in the area first.

• Never hit a zombie pig man.

• Hide from ghasts, and if you must kill them, take a fishing pole.

• Use guerilla tactics to gather glowstone.

• When noob towering after high glowstone, come down when you first hear the ghast shoot.

• Be especially careful when tunneling in the nether.

• Always carry plenty of wood.

• Put glass over deep pits.

• Keep your base and tunnels and any caverns you explore well lit.

• Look around you every once in a while, especially if you hear footsteps.