The most common cause of creosote buildup in a chimney is not burning the wood stove or fireplace hot enough to get the temperature up in the flu.
When the temperature of the flu is too cool and not hot enough then condensation can buildup in the chimney which leads to creosote.
Also burning wood that is not fully cured or seasoned such as green wood or wood that still contains some moisture can be a cause of creosote buildup in a chimney.
Chimney fires are caused by too much creosote buildup that then gets burnt and caught on fire from the heat and fire in the chimney.
You should make sure you burn the wood stove or fireplace hot enough to keep condensation and creosote from building up.
Also have your chimney swept every year before each burning season starts because it's best to have a clean chimney and it's cheaper than losing your life or losing your home to a house fire.