"I knew how I wanted to look" It sounds like the speaker has a goal of changing their appearance, whether it be their body, clothing, or something else about the way they look. We could explore this further by adding on to the sentence: "I knew how I wanted to look, so I started running every day." (Idea is to lose weight) "I knew how I wanted to look, so I bought this new cardigan." (Updating wardrobe) "I knew how I wanted to look. This makeup just won't cut it." (Idea is she is unhappy with her brand/make-up choice)

it means,that you knew( past simple) what clothes you wanted(past simple) put on, or make hairdress in past time . For example I knew how i wanted to look last week, so i put on the black suit