First..... the blower A little hand held puffer to blow the dirt off, sensor facing down (and optimistic gravity will help). You can puff away. Take a shot of a really bright object that fills the screen and have a look at your image to see if you still have dirt in the same place.
Second.... the brush A brush that sweeps or dislodges the dirt and then you puff it off for sure, again sensor facing down. Sweep in one direction and puff after every sweep. And then take a sample image. If you still have dirt and it is in the same place then it needs something serious.
Third... the chemical swab A little swab, made from a microfiber material on a little stick, either pre-impregnated with methanol or methanol to be added. This removes stuck on particles....to be then swept with the brush and puffed off with the puffer. This can......if really bad.....take ages. I know. And now it is part of my routine to take a few shots and make sure there are no sensor marks before I commit to some serious imaging. And I also have some “keep it clean” habits I certainly never had before. My lessoned is learned. Clean results…