The underground is the most recommendable transport to take in order to arrive at the stadium. Which are the nearest stations to Mestalla?
Aragon Station (line 5)
Facultats Station (line 3)
These two metro lines allow you to arrive at the stadium, and get out of it, not only from many areas in the city of Valencia, but also from its surroundings.
Besides metro, you can get to Mestalla Stadium by bus (32, 71, 10, 12, 80, 41, 79, 29, 30, 31, 81, 89 y 90) and by train.