The currency found within a world is often overlooked when worldbuilding. This is because the parts of a story containing the usage of money are often skimmed through. There have been a few instances where non generic forms of fantasy currency have been used such as in The Kingkiller Chronicle by Patrick Rothfuss, but these instances are rare at least in the fantasy I read. In fantasy stories I often find generic gold pieces or coins, and in science fiction I often see the usage of credits.
If you want to create your own currency the first thing you need to decide is what you want to call your currency. All currencies in the world have some form of distinctive name such as yen, dollar, or peso, so you need to come up with your own name. The next thing you need to decide is what pieces are present in your currency and how they differ from each other. For instance coins can differ in the metal used, size, and shape, and there are usually several types of coins with different values. The final thing you need to decide is if the coins in your currency have images engraved in them, or if they have any other identifying features.