The short, sourced answer
The American Academy of Dermatology recommends washing makeup brushes every 7–10 days. After cleaning, dry them flat with the bristles extending beyond the counter edge rather than standing them upright. Read the full AAD instructions.
Give the habit a place
Separate clean and used brushes, and add a clearly named reminder to the day you normally organise your things. ‘Brush care’ is easier to notice than a vague ‘tidy up’.
More isn't the goal
Look at which tools you use before expanding your collection. An unused brush doesn't need to create another step in your routine.
The illustration shows beauty tools, not a drying demonstration. This is general information, not a diagnosis or a substitute for professional advice about a skin concern.