Smile at She had to smile at his enthusiasm. 她觉得他的热情很可乐。（=She was amused by it.）
Smile about：值得笑的（事情） I haven’t had much to smile about lately. 我最近没什么值得开心的事情。
Smile to yourself Mark read the message and smiled to himself. Mark读了信息会心一笑。
要注意咯，smile at yourself不一定真的是微笑出来的，也可能是觉得feel pleased觉得开心。
(Fortune, the gods, etc.) smile(s) on somebody：这是一个文艺说法，是说某人交好运。 If fortune smiles on you, you will have good luck.