Goldfish malady.?

I have recently acquired a goldfish. He's about 2 inches and your normal common ol' goldfish. I've never kept fish before and would like some advice. He's got a bit of fin rot so I put drops in the water for that. He's in a tank - I'd guess it's about 2 gallons. There's gravel in the bottom and a little ornament, which he seems to like to hide behind.. he's shy! I change about 20% of the water every other day. I feed him about twice a day with a little sprinkle of flakes. I have only had him about a week and want to ensure he leads a happy, enriched goldfish life. Any advice?