It is a good feeling of a job well done, so you should start with preparing for the job making sure you have everything you need before you start. Choose your container, making sure there is proper drainage in the bottom.
The soil choice should be of good composition with a percentage of sand, silt, and clay, plus the ability to drain and penetrability to water. Soils to be used may be a combination Pro-mix or soil-less mixes. Hard compacted soils do not produce healthy plants, as roots have trouble growing and taking in nutrients.
Whether you choose a combination of flowers and vegetables for your container, maybe all one color, or all one variety always plant the taller to the middle and cascading plants to the sides.
Fertilizing your container is important and should be done weekly, unless otherwise specified. Being in a restricted space, the plant is relying only on you, as its roots cannot seek further than the sides of the container. Nitrogen being water soluble, the container can be watered from the top giving the roots a good feeding straight through with dissolved nitrogen coming out of the bottom.
A good source of trace nutrients for plant growth is a fish-emulsion with seaweed, Miracle Grow or Shultz. Depending on plants in your container other fertilizer can be used such as slow release granules mixed in the soil or new potting mixes cam be purchased with fertilizers already in the soil mix. Some fertilizers are formulated for certain types of flowers, fruit or vegetables.
According to the plants in your container, some require more water than others. It is important that the water makes its way all through the container to the bottom at each watering to reach all the roots. There can be a tray placed under the plants to catch the extra.