‘No’ is いいえ in Japanese but it may not work in the context below:
Do you want to eat sushi?（すしを食べたいですか。）
No.（いいえ。）
The good expression, instead of just saying いいえ, is だいじょうぶです which means ‘I am fine’. It would be even better if you can add ありがとう which means ‘thank you’.
Do you want to eat sushi?（すしを食べたいですか。）
No. I am fine. Thank you.（いいえ。だいじょうぶです。ありがとう。）