One thing and the most important thing in my opinion is Live Rock. You want to add as much live rock to your tank, and I would add Live Sand to the refuge as well with more Live Rock. If you have some type light I would add some type of Macro Algae. I have a friend who has a 12g tank and has had it setup for well over a year. He keeps it way over stock and it looks great!! He has not lost one fish in almost a year, no algae but coraline and his nitrates are always around 5. I would never do it but he has and he says it is because of how he has it set up and he does weekly 20% water changes.
In his 12g tank he has 25 pounds of live rock 15 pounds of live sand and has live rock in the back chamber. He also uses Purigen which is what I use.
Also do weekly waters or no less than bi-weekly and you will be ok.