I like to make a strong batch of healing herbal tea to put on my skin. You do this by letting the tea steep overnight, or for at least eight hours. Then strain. Then, using a soft cloth saturated with the tea, lay it on your skin where the psoriasis is present.
My favorite teas to use are burdock root and Oregon grape root. Boil the tea briefly and then let it simmer for at least 20 minutes, to get the essential constituents out of the herbs. Make sure the tea has cooled down before applying topically. You can get these herbs in bulk at a health-food store, online, or you may have an herbal apothecary close to you.