As an Erasmus, you can get some priviledges. If you register in some groups on the internet, you can ask for your Erasmus card. This will give you some discounts in bars, shops, restaurants but it also will give you access to Erasmus parties and organized trips to Madrid, Salamanca and Ibiza of course!
Here are two groups where you can become a member. You need to specify your home university and host university, the time you will spend in Valencia, your year of graduation and add an ID picture. They will then contact you to tell you when you can pass by their office to pick up the card.