觉得一件事是好主意，就说 should + 动词；觉得不是好主意，就说 shouldn't + 动词。
should / shouldn't + 动词
You should read this book.
You shouldn't stay up late.
试一试: Man: I don't have much money this month. Woman: You ___ buy lunch every day. 选出那位女士会说的话。 (should / shouldn't / didn't) 答案: shouldn't — 每天买午饭要花很多钱，所以她说他不该每天买：shouldn't。
Should I …?：我该……吗？
想听听别人的建议，就问 Should I + 动词。
Should I wear a jacket?
试一试: Yasmin: ___ study here or at home? Lars: Here. The third floor is really quiet. 选出 Yasmin 会说的话。 (Should I / Why don't you / Could you) 答案: Should I — Yasmin 想听建议，所以她问 Should I study here?
Why don't you / we …?：你/我们何不……？
Why don't you + 动词，是给别人出主意。Why don't we + 动词，是给你和对方两个人出的主意。
Why don't you ask your teacher?
Why don't we walk?
试一试: Man: I want to learn to cook. Woman: ___ take a cooking class? 选出那位女士会说的话。 (Why don't you / Why don't I / How about) 答案: Why don't you — 上课是她给他出的主意，所以她说 Why don't you take a class?
How about + -ing?：……怎么样？
How about + 动词-ing 是用来提建议的。
How about watching a movie?
试一试: Woman: What do you want to do on Saturday? Man: ___ going to the beach? Woman: Great idea! 选出那个男人会说的话。 (Are you / How about / Why are you) 答案: How about — 她说 "Great idea!"，说明他提了个建议：How about going to the beach?
It's a good idea to …：……是个好主意
It's a good idea to + 动词，说的是做什么比较好。
It's a good idea to take a map.
试一试: Man: I want to run in the park every morning. Woman: ___ start slowly. 选出那位女士会说的话。 (It's not a good idea to / It's a good idea to / You shouldn't) 答案: It's a good idea to — 他才刚开始跑，所以她说 It's a good idea to start slowly。