I am often asked by new hobbyists at ABC Aquarium the same one question. For the longest time I avoided a direct answer fearing coming off vague. But now I feel maybe there is the all in one answer to most aquarium related problems new hobbyists may run into.
Q. What is the one most important tip for a new aquarium owner? A. - Waste Management.
This fits both fresh and saltwater tanks and can lead to understanding most issues new hobbyists face. Its a trick answer. Because in a closed ecosystem such as a fish tank everything is linked together, WM can apply to many things. Not just "CLEANING." We are talking about understand the Nitrogen Cycle, proper fish stocking and introduction, feeding, filtration and other equipment, chemical dosing, algae control, live plant and coral health, coral color, fish growth and yes even water changes and aquarium cleaning.
I guess the main lesson is not to generalize things too much. Making everything seem and sound simple may lead to misunderstandings. So the best advice is learn everything about your aquarium and proper maintenance or allow us to help you maintain your tank.