The quickest way to level Smithing is to create Iron Daggers.

Using the Blacksmith Whiterun, purchase Iron Ingots from her, and buy the leather too.

You can then use these materials to create Iron Daggers over and over, sell them back to her and then rest 48 hours to repeat the same process.

This can be expensive but Gold is easy to come by in Skyrim.

You can also use this method to make easy gold.