The Mexican, who made his move to the Spanish club from Arsenal permanent in the summer, has scored four goals in five games in the new campaign.
"I feel good physically. And thanks to that I'm having the best start to my career," he told reporters at a press conference.
"Hopefully I can keep it going and have a great season all round. That way I can contribute in the best way possible to my team.
"I demand the best from myself every day. I don't really set goals for myself, I just want to help out."
Vela helped Sociedad into fourth position in La Liga last season, securing a Champions League place in the process.