Angle of incidence equals angle of reflection...
In other words, you point a camera dead into a mirror and you see yourself, but as you move the camera further off-axis, your reflection falls further off-camera. Longer lenses can help reduce the field of view and thus how much of the space is reflected while also allowing you to be farther back from the mirror. But the angle of reflection rule still applies.
Sometimes you can get away with being at a lower position so your reflection falls below the bottom edge of the mirror. Sometimes you can get away with the foreground subject blocking the reflection of the camera (although it also blocks the view of the camera equally.)
Anything really tricky starts to involve special effects or in some cases, hiding the camera behind a partial mirror so that what's reflected is another mirror.
Look at "Peggy Sue Got Married" -- the first and last shots. In the first, the camera dollies back from Kathleen Turner's face until it is shooting over her foreground shoulder as she sits in front of a vanity mirror -- this required a "fake" mirror (a window) and a double matching her movements to Turner's as they faced each other (think "Duck Soup"...), with all the props on the table duplicated on both sides of the "reflection".