what should i make out of diamonds in minecraft?

Answer 1

Best to hold onto your diamonds until you actually need them. The only thing that a diamond standard is needed for is for mining obsidian, so a diamond pick is the best

Answer 2

If you have lots of them you can make tools, mainly pickaxes. Swords might be worth it anyway, as they are better for killing mobs/PvP. You should not make diamond armour, as it's too expensive. Stick with iron.

Otherwise, if you're playing singleplayer or somehow are protected from griefing, you could use it for decoration.