告诉别人该做什么、菜谱步骤、指路、下指令时，只用动词原形，不加 you，也不加 -s：Add the salt、Turn left、Send the report。
每条指令都用动词原形
Add the flour and mix well.
Turn left at the lights.
Boil the water in a large pot.
Not "You add the salt, then turns left." — say "Add the salt. Turn left.". 不加 you，也不加 -s，只用动词原形：Add、Turn。
试一试: A recipe step: "___ the vegetables for five minutes." (Cook / You cook / Cooks) 答案: Cook — 指令只用动词原形：Cook the vegetables.（把蔬菜煮熟。）“You cook” 多加了指令里不该有的 you，“Cooks” 又多加了指令里从不出现的 -s。
Don't + 动词原形
告诉别人不要做什么，用 Don't 加动词原形开头。
Don't forget your keys.
Don't cross on a red light.
Don't worry, there is plenty of time.
Not "No forget your keys." — say "Don't forget your keys.". 否定指令是 Don't + 动词，绝不是 No + 动词。
试一试: A sign on the door: "___ forget to bring your ID card." (Don't / No / Not) 答案: Don't — 告诉别人不要做什么，用 Don't 加动词原形：Don't forget.（别忘了。）“No forget” 和 “Not forget” 是照搬了别的语言的说法，英语这里要用 Don't。
Please + 动词，表示礼貌
让指令更礼貌，就在开头加 Please，动词还是保持原形。
Please sit down.
Please arrive by 8:45.
Please go to reception first.
试一试: At the front desk: "___ sign your name here." (Please / Pleased / Pleasing) 答案: Please — 指令开头表示礼貌的词是 Please：Please sign here.（请在这里签字。）“Pleased” 是“开心”的意思，比如 pleased to meet you，“Pleasing” 是形容让人愉快的东西，这两个都不能用来开头表示礼貌的指令。
Do + 动词，听起来更温暖
在动词前加 Do，可以让语气更温暖、更鼓励人。这会让邀请听起来更有力、更友好。
Do try the cafeteria, it is excellent.
Do have a great first day.
Do come in and make yourself at home.
试一试: A friendly office email: "___ try the cafeteria, it is excellent." (Do / Does / Doing) 答案: Do — 想让语气温暖又有鼓励感，动词前面加 Do：Do try the cafeteria.（一定要试试自助餐厅。）“Does” 加了这个句型里从不出现的 -s，“Doing” 是 -ing 形式，不能用来开头下指令。
给步骤排顺序的词
按顺序说步骤，先用 First 开头，接着用 Then 或 Next，最后一步用 Finally。
First, boil the water. Then, add the pasta.
Next, stir well. Finally, serve hot.
First, log in. Then, click Settings.
试一试: Turn off the oven. This is the last step, so start it with ___. (Finally / First / Then) 答案: Finally — Finally 表示最后一步：Finally, turn off the oven.（最后，把烤箱关掉。）“First” 是用在开头的，“Then” 是用在中间步骤的。
试一试: Starting a set of directions: "___, go straight. ___, turn left at the bank." (First … Then / Finally … First / Then … First) 答案: First … Then — 第一步用 First 开头，下一步用 Then：First, go straight. Then, turn left.（先直走。然后左转。）Finally 该用在最后一步，不是开头。
试一试: A recipe card says: "___ add the salt now, but ___ let it boil over." (Do … don't / Don't … do / Do … do) 答案: Do … don't — 前半句是温暖地鼓励人去做，所以用 Do add the salt.（一定要加盐。）后半句是提醒要避免的事，所以用 don't let it boil over.（别让它煮溢出来。）Do 用来友好地推一把，Don't 用来提醒该避免什么。