[bread_baker]

They need to learn the vocabulary for their jobs. If they are carpenters, they need to know all the names of the tools, as well as some relevant verbs. This has to be priority. You can use this vocabulary with the grammar you teach them.
Simple present:
Is this your toolbox? Yes, it is. OR No, it isn't.
Present continuous:
What is Peter doing?
He's installing some cabinets.

Don't teach them too many new words each day. How many words, you ask? Some teachers are very conservative. Definitely not more than 10 each day, and some teachers teach fewer. You will need to give them practice of the same words over a number of days. It takes a lot of practice over time for the words to "stick." You may also want to give them spelling tests. Then they have to learn how to spell the words. Depending on their jobs, they may also need to learn how to report accidents, defective or broken equipment, etc. This means they need to learn how to fill out forms and write legibly.