Growing bonsai (pronounced "bone-sigh") is not extremely difficult.
Bonsai do, however, require daily attention during their growing seasons.
Knowledge of one's trees' particular requirements, basic techniques for
maintaining a tree in a small container, and patience are also necessary.
The choice of tree to purchase, for one's self or as a gift, is very important. Outdoor, winter-hardy trees will generally not thrive indoors. Most of these need the bright sun, air, humidity, and even winter dormancy to be healthy. These conditions are extremely difficult to reproduce indoors; a popular first bonsai is the Japanese Green Mound Juniper (Juniperus procumbens nana), and many die from casual treatment as an indoor houseplant.
Tender species, including "tropicals," even thrive outdoors in the warm months, although they must spend winter indoors. Supplying sufficient light and humidity even for these is also challenging, but possible.
A common cause of tree loss is overwatering. Many assume wrongly that since the tree is in a small pot, it must be watered constantly. Depending on the species, its condition, type of soil, size of pot, location, etc., watering requirements might vary from twice daily to once weekly. In general, the soil should be dry a half-inch or inch deep before thoroughly watering. If a very fine-spray bonsai watering can is not available, the entire pot can be immersed in water; other methods will wash soil particles out of the pot. Frequent misting of foliage, however, does not contribute to soil problems, and is a good method for increasing humidity.
A common error is to fertilize an unhealthy tree, believing undernourishment to be the problem. Trees seldom die of starvation, but a problem with the root system will be made worse by fertilizing, and the tree will only die more quickly. Never fertilize a sick tree. There are, however, hormone and vitamin products which can sometimes help stimulate a tree to recovery and are safe to use.
The beginner does not have to purchase an expensive specimen; there are "starter" bonsai available at reasonable cost, becoming more common at local nurseries (avoid department store, glued-rock "bonsai", except as a gamble). One can even create one's own bonsai trainee, from ordinary nursery stock plants.
Soil components are very important. A good practice is to sieve all soil components to remove small particles, improving drainage and air spaces, and prevent over-watering, root rot, and subsequent death of the tree.
Expensive tools are not needed to start; while the various bonsai tools each have their specific purpose which they do well, the beginner can use common tools, and improvise others, obtaining specialized tools over time as interest grows. Examples:
Hard-to-find or expensive bonsai pots are not required to begin;
bonsai can be trained in almost any container, or in the ground, and will
actually benefit from being trained in a larger soil volume. Later, appreciation
of the tree will be greatly enhanced by the appropriate container.
Trees grown in small pots must be repotted occasionally, perhaps yearly. How often, again, depends on many factors. It is best done at the end of a dormant period --- for example, late winter/early spring for outdoor trees. A recently repotted tree must be protected from direct sun, wind, and freezing temps, and not fertilized, until new growth is evident, usually about a couple of weeks.
And if one does lose a tree... don't give up. Try to learn what went wrong, and try again. Although not commonly displayed, there have been a few dead trees in every collection.
For more information on bonsai, visit a nursery which sells bonsai and supplies; your local Public Library may have quite a few books on the topic; or try to find a local bonsai club thru the rec.arts.bonsai newsgroup on the Internet, or thru local nurseries or community botanical garden.