It takes a lot of patience and repetition with instructions. Some days my husband will listen and other days he just doesn't understand. These are the times, I just have to walk away for a while, and try again.
Patience and trying not to expect something they aren't able to achieve any more. Don't ask or expect too much. Let them decide what they think they are capable of doing at that moment and let the rest go. Step in when necessary, but not before it is necessary.