Fill the aquarium with water and add some dish soap. Using a soft cloth, clean the aquarium thoroughly. Discard the soapy water and rinse well, and make certain to remove all trace of soap. Dry and polish with a soft cloth, or discarded dishtowels.
Place a 1-inch layer of gravel inside of the aquarium, covering the bottom entirely. Add an even layer of activated charcoal on top of the gravel, bringing it up to about one inch.
Fill the aquarium with high quality potting soil until it reaches within 5 to 6 inches from the top.
Plant either seeds or seedlings in the soil. You can purchase miniature tools for container gardening, or use an old spoon or fork. Water sparingly, taking care never to over water. When in doubt, remember it is better to use too little rather than too much water.
Move your aquarium into the sunny spot you have chosen. Your mini garden should start to flourish within a week.