Common expression: "What we do is we...." You might also hear or read this as "What we do first is we...."

An example: "What we do is we take down our pictures."

The problem: Think of the "is" as an equal sign. In this example, "what we do" equals "we take down our pictures." This seems correct, but it is not. "What we do" refers to an action, so whatever is on the other side of the "is" should be the action, not "we."

The correct version: "What we do is take down our pictures."

Other correct revisions are possible. What's yours? Do you have a different example to share?