There are many types of skin disease with different causes and triggers. If you think your pet has a skin problem, please seek veterinary advice. 
Parasites are one cause of skin problems and controlling Fleas and Ticks and mites which can trigger skin disease is very important and Prescription medications are the best products for this. 
Allergic skin disease is common in dogs and often seen in cats too. Food trials for 8-12 weeks with a hydrolysed diet for allergies is a way of determining if a food allergy is involved in skin disease.  
If it is your pet can either then stay on the food or you can try introducing a new food, one at a time to work out what triggers the allergy and what you pet can happily eat. 
Some pets require prescription medications including medicine to help reduce the itchiness and inflammation. 
Shampoos and mousses or foams can help reduce secondary bacterial or yeast infections. What your budget is for these products is obviously a factor but the more expensive ones on our website are the most effective and are what vets recommend. 
Nose and paw balms will help dry or cracked noses or pads. 
Supplements are available too which may help skin inflammation. Supplements have been anecdotally thought to help although there is no evidence based research to confirm this