It depends on what type of aquarium you want. With a 30 gallon tank there is wide variety from a specific type of biotrope (Amazon, Asian, cold water, etc.) to species tanks (cichlids, etc.) to community tanks. The type also depends on your experience level and how much work you want to do as well. For some inexperienced, the Amazon tanks work as the fish are relatively hardy and do not demand an extraordinary level effort once the tank is established.
As for plants I'm partial to easy, low tech live plants. To me it makes for a better looking tank in the long run and helps with your water quality.