...Play
Minecraft in Survival mode.
Seriously.
When you start out you spawn in a random place in a sandbox(humungous and where everything is interactive) world made up of blocks of different stuff - grass, dirt, wood/leaves(trees), water, lava, cobble, sand, ores, etc... You have no weapons, no home, no tools, no food, no map, no clock... You have to hunt for your food or you get hungry and your health doesn't regenerate, and every night there's a load of shit that wants to kill you. If you die you lose all of your stuff and respawn in the same place as before.
The more you advance, the less you die and the more interesting stuff there is to do.
