1. Use the indirect method. Instead of saying “I can’t do this”, you can say “I am busy today”.
不要太直接。与其说“我做不到”不如说“我今天很忙”。
2. Dislocate yourself. Don't say "I can't eat this", just say "My big brother says it is harmful for health etc.
不要提你自己。别说“我不吃这个”，要说“我哥哥说吃这个对身体不好”之类的。
3. Handle it with tact. Example: "I love flowers, when I will be free I would definitely bring them. But I can't bring them right now."
说话要圆滑。比如：“我挺喜欢花的，如果有时间的话，我肯定会带一点回去。但是现在恐怕不方便。”
4. Be quiet. Sometimes only becoming quiet is enough. People will know that you are not going to do what they have asked you to do.
沉默。有时候沉默就足够了。别人能够从你的沉默中知道你不会去他们要你做的那件事情。
5. Just speak up. People would feel annoyed but later they would realize your position.
直接说出来。刚被你直接拒绝的时候，别人也许会觉得不爽，但是过一会儿他们就会了解你的立场。