Mirror plays an important role in Vastu, so placement of mirrors are very important. Mirrors can make or break energy within your house. The incoming positive energy mainly depends on the way mirrors are placed in your home.
If your mirror is placed such that it reflects the main door, Vastu suggest that this would send out all positive energy thus making you miss out on a lot of opportunities. Mirrors, shining or glass objects are clear no in front of the main door.
you can read info related to mirror and its placement in the below link