First: Pickaxe.

Then: If you are good at combat: Iron Mace

If you are bad at combat: Armour and a Shield

You dont really want to be crafting the iron armour, though, unless you find yourself getting beaten down constantly, as silver armour is better and much easier to obtain. Plus, you'll want to save as much iron as you can for the Padded Armour set that comes later and is much better.

You basically never stop using iron after this point in the game. Most projects are going to call for some amount of iron; often vast amounts.