なおす is the most plain, and also natural word when to make something correct, fix or cure. In other words, getting something to be its right/natural state. Note that we use various Kanjis for なおす to make it clear how to do so. ex. correct or fix -> 直す; cure->治す
正す/ただす/ is often used with some certain nouns, like 姿勢/しせい/を正す (adjust posture)、不正/ふせい/ を正す (right a wrong).
矯める is a big word, we rarely see.