be careful (doing something)

Say this when giving advice about something difficult or dangerous, where someone should take extra care.

Be careful answering the multiple choice questions. They’re trickier than they seem.

Be careful coming around the corner up there. Cars can’t see you.

(something) isn’t steady

You can say this about something that moves a little when you push it or step on it.

Oops! This table isn’t steady. Can we put something under the leg?

Watch out-- that floor board isn’t steady.

You should also know the phrase "hold (something) steady":

Lay it on its side and hold it steady with your other hand. It's easier to cut that way.

step on (something)

To "step on" something means to walk or run on top of it:

I think I stepped on a piece of gum.

Note that we only "step on" things with our feet. In a car, you "run over" something:

I ran over something that fell out of the truck in front of me and it popped my tire.

With your body, you "roll over" something:

Some parents don't want their babies to sleep with them because they're afraid of rolling over them.