One of the most common issues is that the door is being opened too fast. This can cause the smoke to be drawn into the room as the firebox has not had time for the pressure to equalise. The smoke will then take the easiest route, which is out through the opening.
This can also be a result of incorrect additional ventilation air into the building (check with your installer).
Release the handle and just allow the door to sit for about 10 to 20 seconds to allow the airflow to be re-established. Then open the door slowly and carefully place the fuel.
Also ensure all fans near the stove (kitchen, bathroom etc.) are all turned off as this can pull the smoke out of the stove.
Cold weather could also be the cause of the smoke. During colder weather cold air can become trapped in the chimney if there is no air flow. Unfortunately, when you then light your fire the colder denser air forces the smoke back down the chimney and out into the room. We recommend putting either a roll of newspaper or a firelighter on top of your wood and this will heat up the chimney and clear the blockage.