The Potty Board !!!
I did this with my daughter and it helped. We went in the bathroom with a digital camera, and took picture of each of the steps involved in going potty. (careful, I am not suggesting inappropriate pictures here).
We had a picture of her sitting on the toilet, with her dress over her lap.
a picutre of her with toilet paper wrapped on her hand -- after we talked about how much to use and what it should look like
We had a picture of her straightening her dress, which represented getting re-dressed.
We had a picture of her flushing; another of her washing her hads; another of her drying them; and lastly, turning out the light.
I arranged them in one document and printed them on an 8 be 10 piece of photo paper, so it was thick, and then made one for each bathroom in the house. She then knew what she needed to do, and the reminder was right in the bathroom. That was all she needed, but you could go the next step of having rewards and consequences when your son does or doesn't follow all the steps.
Lastly, if he is on a "'am big now" kick, you might want to try showing him how you use lists to remind you of what you need to do. Then he may see the Potty Board as being like your grown up list.
It might help. Best of luck!