The phrase "picks up" means "becomes busier":

I sure hope sales pick up soon, or we're really going to be in trouble.

Things always pick up around the holiday season.

Use "pick back up" to mean "become busy again"

Now that it's picked back up again, I'm starting to consider hiring another person.

You can see some of the common subjects of "pick up" in the examples above:

• it
• sales
• things

Other common subjects of the phrase "pick up" include:

• business
• attendance
• the economy
• the wind