1. When I was seventeen, I made the decision to come to the U.S. to study.2. If you decide everything on your own without discussing it with others, you are likely to get in trouble.3. He loves to do things his own way and nobody like that.
 make one's (own) decision; decide on one's own do things one's (own) way請參考例句.
1. 我十七歲時自作主張到美國來唸書.2. 你凡事自作主張不跟別人討論, 很容易吃虧.3. 他是個很自作主張的人, 很不得人緣.