Step 5: After every shower, hang the corner of the curtain on the hook on the wall
HOWEVER shower curtains, like tubs and walls, get splashed with whatever you are washing off you...and soap...and shampoo... etc etc. So, like tubs, they DO NEED regular cleaning - especially the bottom edge on the drain end because everything drips off that corner.
Cleaning isn't hard... just remove the ring from the corner, take down the curtain, and toss it into the load when you wash sheets.*
If you have hard water, wash the curtain more frequently, and from time to time soak the curtain in a bucket of water with a cup of white vinegar before running it through the wash. Don't worry, the vinegar smell will wash out.
*If you use solid vinyl curtains, remove the ring from the corner holes, take it down, and wash it on hot wash and hot or warm rinse with detergent and old towels (towels do the scrubbing). Don't leave it alone during the draining cycles because if the curtain traps water, the washer may get off balance. DO NOT use cold water at any point... the curtain will shatter. If it has cooled and gotten stiff when you remove it from the washer, put it in your bathtub and run hot/warm water over it until it is soft enough to rehang.