To tell someone what to do, a recipe step, a direction, an instruction, use the base verb alone, with no you and no -s: Add the salt, Turn left, Send the report.
Each instruction uses the base verb
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.". No you and no -s: just the base verb, Add, Turn.
Try it: A recipe step: "___ the vegetables for five minutes." (Cook / You cook / Cooks) Answer: Cook — An instruction uses the base verb alone: Cook the vegetables. "You cook" adds a you that instructions leave out, and "Cooks" adds an -s they never have.
Don't + base verb
To tell someone not to do something, start with Don't and the base verb.
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.". The negative instruction is Don't + verb, never No + verb.
Try it: A sign on the door: "___ forget to bring your ID card." (Don't / No / Not) Answer: Don't — To tell someone not to do something, use Don't and the base verb: Don't forget. "No forget" and "Not forget" copy the way some other languages say it, but English uses Don't here.
Please + verb, to be polite
To make an instruction polite, add Please at the start. The verb stays plain.
Please sit down.
Please arrive by 8:45.
Please go to reception first.
Try it: At the front desk: "___ sign your name here." (Please / Pleased / Pleasing) Answer: Please — The polite word at the start of an instruction is Please: Please sign here. "Pleased" means happy, as in pleased to meet you, and "Pleasing" describes something nice, so neither one starts a polite instruction.
Do + verb, to sound warm
Add Do before the verb to sound warm and encouraging. It makes an invitation feel stronger and friendlier.
Do try the cafeteria, it is excellent.
Do have a great first day.
Do come in and make yourself at home.
Try it: A friendly office email: "___ try the cafeteria, it is excellent." (Do / Does / Doing) Answer: Do — To sound warm and encouraging, the word before the verb is Do: Do try the cafeteria. "Does" adds an -s the form never takes, and "Doing" is the -ing form, which does not start an instruction.
Words that put steps in order
To give steps in order, start them with First, then Then or Next, and the last one with Finally.
First, boil the water. Then, add the pasta.
Next, stir well. Finally, serve hot.
First, log in. Then, click Settings.
Try it: Turn off the oven. This is the last step, so start it with ___. (Finally / First / Then) Answer: Finally — Finally marks the last step: Finally, turn off the oven. "First" is for the beginning, and "Then" is for a middle step.
Try it: Starting a set of directions: "___, go straight. ___, turn left at the bank." (First … Then / Finally … First / Then … First) Answer: First … Then — The first step starts with First, and the next step with Then: First, go straight. Then, turn left. Finally would be for the last step, not the start.
Try it: A recipe card says: "___ add the salt now, but ___ let it boil over." (Do … don't / Don't … do / Do … do) Answer: Do … don't — The first part gives a warm push to do something, so Do add the salt. The second part warns against something, so don't let it boil over. Do for a friendly push, Don't for what to avoid.