My dogs are on a kibble rotation and I always supplement with 1000 mg of human grade salmon oil each day. I also give a teaspoon of unrefined virgin coconut oil every other day which I feel particularly helps with dry skin.
Our dogs get fish oil supplements every day. We use the human grade Spring Valley brand. They are 1000-mg tablets. We get it either at Wal-Mart or Target. Tucker started to get a little bit of dry, flaky skin last winter and the fish oil tablets helped significantly and he has been on them ever since. It's also great for their hearts and can help prevent some cancers, so I would still give it even if my dogs weren't prone to dry skin.