Another thing you can do to achieve a clean paint job is to use a degreaser to clean surfaces before you start. This works wonders for removing grime on the wall (or whatever surface you're painting). A degreaser works by dissolving the oils and dirt stuck on the walls without leaving behind any residue. This goes a long way to ensure the paint adheres better to the wall once applied.
It's also worth noting that cleaning surfaces with a degreaser first can also help preserve your paintbrushes, as they won’t get as overloaded with dirt and debris that can damage them.