One thing that is a requirement in this life is to have companions to talk to, enjoy the company of, and to share ideas with. Although sometimes finding the human variety is not so easy and if your in a small town where everyone you know is very busy, you may want to find a new kind of companion: a pet. Pets bring us joy and give us the opportunity to exploit our love of taking care of something and bringing a better life to an otherwise ordinary fish, for example.
If your just bored and want something interesting to do, or your having a problem dealing with social anxiety, you can at least help yourself to feel a bit social, in practice, by purchasing a fish and talking to it. By taking care of a fish, especially if you like a challenge and want to get a salt water fish (which take a great deal more to take care of it) you can move your mind in a better thought stream. In a way the simplicity of a fishes life can reflect upon you the awareness that no matter how complicated life gets, how anxious you feel, everything will always work out.
If you simply want a hobby that is rewarding and meditative, even therapeutic; then purchasing an aquarium can be a great deal of fun and rewarding. When purchasing an aquarium there are many things to be aware of first. First you need to take into consideration what your goal is. Do you want one small stand alone fish? Do you want a school of fish? How about several different fish that get along?
You should think ahead about 6 months and ask yourself if you want a bigger tank (so you can get more fish and spend less money up front vs purchasing a small tank then later having to upgrade it) or just a small tank and a few small fish to take care of. If your undecided the best thing to do is to get the smaller tank so you can get a feel of how you like having a fish and taking care of one.
A larger tank is going to take more work. Once or twice a month you will have to take everything out of the water: rocks, fixtures, filters, fish, and anything else submerged in order to clean them off and put it all together again. This can take from one hour to several and is a bit tedious until you develop a system to do it efficiently.
If you like having a lot of fish or some exotic fish that need a lot of room, then the bigger tank is the best option. If you just want a small tank and a humble fish that is easy to take care of (or to get used to the idea and ease into owning a fish) with just one beta or similar "pretty" fish, then the small tank is best. Within the sizes there are many types of tanks from small fish bowls to rectangular medium sized (and cool to look at) tanks.
Whatever you decide, you will find that taking care of a fish is a rewarding experience. Many think that taking care of a fish is good luck, others love to have water flowing in the rooms of the home for feng shui (water elements). Just reading up on the ownership of a fish can be a fantastic experience. It's a great cure for loneliness and boredom respectively!