Tipping servers in restaurants and cafés in Spain, while appreciated, isn't mandatory. It's tough for Americans to get used to not leaving a tip, but locals generally don't leave anything extra at all in more casual eateries. In fine-dining restaurants, a tip may already be included in the check.
Do waiters come to you in Spain?
In Spanish culture, a good waiter leaves you alone until you specifically call him or her over to the table.