What is the best way to promote a patient's independence when bathing a patient who had a stroke?

Start small! If they still have mobility in one side, or both sides, or certain areas of their body, have them try to do some of the bathing themselves. If they can move their left or right hand, try having them wash down the other hand that they cannot move, thus showing them that they still have a level of normalcy. Then move on to something more complicated, like washing feet or their face or their other arm. In a patient who has full mobility you could even have them wash their shoulders or hair. If you have a patient with extremely limited mobility, as they are going through exercises and physical rehabilitation you could have them hold things, or wash themselves, thus showing that they can still function independently. As time goes on and they are praised for their achievements, they will want to gain their independence more, and they may make headway of their own. Just remember to start slow and small, so that even if they cant do it or cannot maintain the action they are doing, they still did something and that is good enough.