Why is my fire smoking?

There are several reasons why a fire may smoke into the room. Check the following points:

Clean the chimney.
If the chimney has been swept, check that the sweep has reassembled the flue system and fire correctly.
Check that the cowl and bird protection is clean and clear.
Check that the flue is not obstructed, e.g. bird nest or other obstruction.
Check that the damper is fully open when first lighting the fire.
New homes are designed for optimal insulation and heat retention and will require a different technique for burning wood fires. Wood burners require oxygen for combustion. With an airtight home, this becomes a problem. And it is exaggerated when kitchen range hoods and extraction fans are used in open-plan rooms, as they remove even more available air causing negative air pressure. The simple solution is to crack open a nearby door or window, especially when the extraction fans are used. You will find user manuals for the extraction fan system give similar recommendations.
Make sure you have enough flue for the fire’s correct up-draft (draw).
If you have made alterations to your home, or there has been further development in the area, e.g. new home or an increase in nearby tree height, this can affect the fire’s up-draft.
Make sure you are producing enough heat to allow the firebox and gather to get hot. The fire will not draw correctly if the flue is cold, and smoke will issue into the room