Well, as long as you don't overfeed, feed quality food, and keep good water conditions then you really shouldn't have any problems. Most fish diseases are caused by poor tank/water conditions, either because water changes are not done regularly enough or the filter/substrate are not cleaned. Granted you don't want a perfectly clean filter because that means you have no beneficial bacteria, but you also don't want excess waste.
By the way, what I mean by poor tank/water conditions causing fish diseases is that fish immune systems get weaker in those conditions and become more susceptible to disease. Most fish and tanks will usually have a variety of harmful bacteria/diseases in them, but as long as the fish are healthy their immune systems are able to fight them. Obviously keeping a good water/tank maintenance schedule cuts down on the proliferation of disease and bad bacteria in the tank, which also makes it less likely the fish get sick.
