My gran and mum have this although I haven't inherited it (I got my dads' eczema instead- WHAT a family of skin complaints!!) at times they keep it well under control, at others it gets them down.
I agree that seeing a herbalist or sympathetic doctor is a good idea if it is getting really bad. However there are a few things they tried that helped and are easy for you if you want to:
Diet- Limit alcohol, refined sugar, animal fats- as you may well be correcting impaired liver function-you need to get toxins OUT of the blood. Increase fibre and coldwater fish (or take fish-oil type supplements like flaxseed oil/cod liver oil)
Take Vitamin A, Zinc, Folic Acid, Selenium
Psychological- I believe most skin problems have a psychological aspect, ie when you are stressed/depressed etc it will flare up. So it is important to take time to REALLY relax, try stress reduction techniques and take some light exercise.
Sunlight- don't overdo it as UVB is bad for your condition but a little sunlight will help as the UVA is very beneficial. In fact I know someone who went to hospital for UVA therapy and it cleared her psoriasis up almost totally! So you may want to ask the doctor about that.
Topica preperations - Ok, my mum and gran never really got away from coal tar based stuff. But I read that you should ask your herbalist or pharmacist about topical preperations with comfrey, licquorice and camomile extracts if you want a more herbal approach (as coal tar has its nasty downsides)
Herbal medicine- again, this is just what I've read, but ask the herbalist about Sarsparilla root and Silymarin.
Hope any of this helps.