Check the easy things first
Confirm the damper is fully open, crack a nearby window to relieve negative pressure, and warm the flue with a rolled newspaper torch before lighting. Burn only seasoned wood — wet wood smolders and smoke stalls instead of rising.
When it is a blockage
Creosote glaze, a bird nest, a collapsed flue tile or leaves on the smoke shelf all narrow the opening the smoke needs. If the fireplace smoked less last year than this year, suspect buildup.
Draft and design problems
A flue that is too short, too wide for the firebox opening, or fighting a taller nearby roofline will never draft well on its own. Height extensions, a correctly sized cap and smoke chamber parging solve draft problems that cleaning cannot.