Learn Portuguese (Portugal): Tu verificas a máquina antes de trabalhar.

In Portuguese, when you use antes de (before) or depois de (after) and the person doing both actions is the same, you follow it with the infinitive. English often uses the -ing form ("before working"), but Portuguese uses the plain, unconjugated verb.

Do I always need the word de after antes?

Yes, whenever "before" is followed by an action (like trabalhar) or a noun, you need the preposition de. You only use antes by itself if you mean "beforehand" or "earlier".

Could I use the verb checar here instead of verificar?

It is highly recommended to use verificar. While checar is common in Brazilian Portuguese, verificar is the standard, natural way to say "to check" in Portugal.

Can I drop the Tu at the beginning of the sentence?

Absolutely! The ending of verificas already tells us the subject is tu (you). Including it just adds a little extra emphasis, like saying "You check the machine...".