| 1st day:
You spawned in a world full of trees, pigs, cows, caves with ores and plains. You must collect wood by punching a tree log until it brakes. Cut down 3 trees (choose short ones for saving time) and convert the log into wood planks by opening your inventory. You do that, by pressing "E". Place the log in the 2x2 square. You will produce 4 wood planks from every log! Make a crafting bench by filling the 2x2 square with wood planks. Make sticks, a pickaxe, get some stone and make stronger tools. If you find sheep kill them to make a bed and skip the first, boring I'd say, minecraft nights! But eyes on the sun's progress among the sky! You don't wanna spend the night without a shelter to hide! A quick shelter could be made inside a hole, which you have dug, to get stone. Don't forget to craft torches though! You don't wanna see zombies spawn inside your shelter!
2nd day: As soon as you see the monsters getting burnt from the sun get out and gather some more wood. Craft an axe and start chopping!!! You can build a house now and get creative. Just don't travel far away from your spawn point unless you got a bed ready. You don't wanna lose your house forever if you die!
The items you should have in your house so you can easily get going:
2 furnaces, a bed, a door (LOL), a large chest, a crafting table and a mine.
1) Never dig straight down! You might fall in a pit of lava!
2) Find a way to mark your way up to the surface if you find a huge cave system!
3) Don't try to mine ores that need a higher pickaxe level (for example: you can't mine diamonds, redstone ore and emerald ore with a stone/wooden pickaxe! You need an iron one)
4) You can find diamonds from ground level 16 and down.
5) Be smart and not engage a fight with a large group of mobs!
6) Try to find a spawner, a ravine or a abandoned mineshaft!
After 3rd day: You might want to make stuff more simple with redstone mechanics like making automated furnace and storage rooms, minecart transportation systems or just go explore some other worlds like the mighty Nether or The End, which is full of the thin black men, the endermen!!!