I try to do mine twice a year. Once at the start of the season and one in January/February depending on how much use it sees.
I purchased a
Sooteater cleaning kit as opposed to using one of the stiff bristled ones.
It's flexible enough that I can put it through the bottom of the stove and push it up the chimney as opposed to having to go up on the roof and work down.
It has been well worth the price and does a great job with no chance of me falling off the roof.