Marcelino's side were promoted to La Liga ahead of this season and have made an excellent start to life in Spain's top flight.
Villarreal currently sit sixth in the table at the mid-season break thanks in the main to a defence that is third-best in the division behind the top two, Barcelona and Atletico Madrid.
Costa has made 14 appearances for Villarreal this season but acknowledges 2014 might not be as good for the club - despite being upbeat about the future.
"Being at the level of this year is going to be tricky," Costa said.
"But we know we have to perform like that if we're going to do well.
"Every year in football is different and every game is different. But we want to be even better in 2014.
"We have shown that we are a competitive team, but everyone is confident that we can go up another level."
