Cleaning with petrol or diesel and then using a bristle wire brush(for main jets) to clean them is recommended. however using compressed air is also sufficient.
Another alternate method, (
which i havent tried yet) is boiling the jets in acidic water. Will be doing those the next time i get the carb out.
To get to the jets. You just need to open the Carb bowl. (Keep fuel cock in off, then drain the carb bowl using the screw drain valve at the bottom of the bowl, if you want to save the petrol in the bowl. then fish out the drain pipe.

)
After opening the carb bowl you will see the main and idle jets. These can be removed using a flat head screw driver.