Construct a Dispenser.

Enter an End Portal.

Use Shears to obtain wool from a Sheep.

Attack and destroy a monster.

Bake a cake using wheat, sugar, milk and eggs!

Harvest some leather.

Throw diamonds at another player.

Brew a potion.

Construct a better pickaxe.

Use planks and sticks to make a sword.

Construct one type of each tool (one pickaxe, one spade, one axe and one hoe).

Craft a workbench with four blocks of wooden planks.

Build some bookshelves to improve your enchantment table.