To be considerate; to pay attention to or worry about something — to take care, be mindful or make an effort to accommodate others.
初対面の相手にはどうしても気を使ってしまう。
I inevitably try to be careful/considerate with someone I meet for the first time.
母は料理に気を使って、栄養バランスを考えてくれる。
My mother pays attention to cooking and considers nutritional balance.
会議中は周りに気を使って静かにしていた。
I kept quiet during the meeting out of consideration for others.
彼女は細かいところまで気を使う性格だ。
She is the sort of person who is attentive to small details.