Clean my ducts at least once a year (usually in the Spring). I rigged up a shop vac that came with the fat suction hose and attached a regular size house hold vacuum sweeper hose to it. It's perfect for getting inside the ducts, shove it down them and suck everything out. It's long enough it almost reaches the next duct. But then you go to the next duct and go back to where you left off, and then go forward to the next one. Works great. It drives me batty to see dust and dirt and crud in those holes. I clean out the area you can see quite often, and it's amazing how much gunk collect in them.
I don't have to worry about ducts in my house, especially in the floor, it's all electric!