The 21-year-old joined from Borussia Dortmund last summer but endured a frustrating debut campaign in west London.
A hamstring injury limited him to 27 appearances across all competitions, including just 12 starts, with the winger unable to feature after January.
The England youth international believes his commitment over the past few months has paid off and is now ready to make a bigger impact for Chelsea.
“It was a real challenge at the start because it was the first muscle injury I have had,” Gittens told Chelsea website.
“It was hard for me, but hopefully I can look back and tell myself that I’ve done well in this situation. I’m feeling much better now. I’m feeling more confident. My hamstring is good.
“I have to keep going now, keep pushing myself, get more minutes in the legs, train myself to the maximum so hopefully I can have a good season.
“I just want to show everyone what I can do. I’ve just shown glimpses so far, I would say, so my objective is to keep getting better, keep working on myself, then this season will be a good one.”