1. relax oneself 放松自己
尽量避免直接说：I want to relax myself.
有点xing暗示，用得不好会有点尴尬
除非你提到具体的动作，比如说：
I would like to watch a movie to relax myself.
我想看一部电影放松自己。
2. 直接说relax即可
You need to sit back and relax.
你得放松一下啦。
I find it difficult to relax knowing I have an exam tomorrow.
知道明天要考试，我觉得很难放松。
3. unwind /ʌnˈwaɪnd/ 放松
Listening to music is a great way to relax and unwind.
听音乐是一个放松的绝佳办法。
I've been really swamped lately. I need a vacation to unwind.
最近太忙了。我得度个假放松一下。
swamped adj. 很忙的／事很多的