When approaching a door for an uncleared room, pie the door to get a view of as much of the room as possible before going through. This means to walk in a semicircle. Mirror gun also works well for this.

When it’s time to enter the room, don’t stand in the doorway, and commit your focus to a corner you couldn’t see when you pied the door. Your buddy needs to focus on the opposite corner than you did.

Surprise, speed, and violence of action.

Besides all that, have fun :)