You want the roots to grow down and deep, rather than shallow and out. Deep roots improve a plant's resistance to drought, and reduce competition with its neighbors. Plants are most vulnerable the first two years after planting, because the roots haven't knit with the soil. This is when protection against cold and competetion from weeds and grass is most important, i.e., when mulching is essential.
Location. Different locations within a plot or even small yard can have dramatically different climates, or "microclimates." Low spots are colder than high ground (cold air sinks), which is significant if a plant's cold-hardiness or chill-requirement is borderline for your region. A north wall may block the low winter sun, but not the high summer sun, which is useful for extending dormancy in plants damagable by late spring frosts but which need plenty of sun during the growing season. (e.g., apricot, citrange). A southern exposure may provide extra warmth. Wise site-selection can make or break borderline plantings. Planting in soggy soil is a popular disaster.
Planting. Dig a whole twice as wide and slightly deeper than what you plan to put in it. If you have any carcasses lying about, now's the time to toss them in. Put the best soil you have in the bottom, to encourage downward root growth. The best soil you have is top-soil unless you get some from elsewhere. Experts disagree on how much compost should be mixed into the planting soil, with opinions ranging from 50% to none at all. In any case, don't make planting mix a lot fluffier or richer than the surrounding soil: the concern is that the roots have reason (roots are very left-brain) to grow beyond the hole you dug. If the plant came bare-root, soak the roots in water for 8 hours. Prune any roots you know are dead. The plant will settle, so set it high in the hole; the deeper the hole, and the fluffier the planting mix, the greater the settling. Fan out the roots in an intelligent, sensitive manner. What would you like if you were roots. Fill the hole with dirt, firmly; don't fill it with airpockets. If the tree is grafted, make sure the soil is several inches below the graft line. Soak. If soil settles after soaking, add some.
Care. In general, water deeply and periodially, rather than constantly and lightly, to encourage downward root growth. Many experts will disagree with that advice (experts disagree as a matter of course: it provides publishing opportunities thus improving job stability). Regular watering is essential during the first season. An inch of rainfall once a week throughout the growing season is about right for plants with average moisture needs in loamy soils. Clayey soil holds water better than loam, sand worse. An inch of rainfall is equal to about half a gallon per square foot; assume that a plant's roots spread 50% wider than its dripline. Even when established, shallow rooted plants such as blueberries need frequent watering; such plants do better in lawns (i.e., frequently watered areas) than others. Mulch keeps down weeds, conserves soil moisture, and insulates the roots: mulch the first year, at least. Fertilize in the spring, if necessary; some experts advise against fertilizing the first year.... Bulky organic fertilizer is safe for the plant, improves the soil, and comes into the world by magic; chemical fertilizer burns roots, doesn't improve soil, and comes into the world by industrial processing. Get the drift? Plants like their food in the outer third of their roots.
Pruning. Some tree structures are sturdier than others, and healthier. Narrow angles formed by vertical limbs are weaker than wide angles and horizontal limbs. Limbs directly opposite each other on the trunk are weaker than limbs that spiral around it. Trees susceptible to water-borne disease and fungi benefit from being open in the center, since it promotes air circulation and lets in the sun. Prune these trees to an "open center," i.e., establish good branching structure and then lop off the central stem right above the top branch, usually 4 to 6 feet above the ground; open center pruning also reduces the height of a standard (non-dwarf) tree the most. A tree pruned to a "central leader" has the shape of a Christmas tree: establish good structure but keep a central stem, heading it annually to promote branching. A modified central leader has a central stem that was headed later in life and higher up than in the open center system. (To "head" a branch is to cut it back to a bud; this induces growth in buds below the cut. To "lop," as I've used the term here, is to remove a branch at its origin.) In most plants, pruning improves fruit quality by reducing the number of fruits (more energy going to fewer fruits); some plants, especially berries, only bear fruit on growth that is one or two years old, and need frequent pruning to maintain productivity. While some plants will require more heavy equipment for pruning, others require a more gentle touch, even to the point of only using a pair of sturdy bonsai scissors to do the job.
The following is a list of some common problems, and no-spray measures to try; for spraying, consult a reliable nursery or other expert. Pesticides posion everything, not just the particular things you intend. In general, to remove fallen leaves and fruit is to minimize pests and disease; bugs overwinter in the decaying leaves and fruits beneath your trees. Burn prunings to keep the doctor away. Usually (but not always) predators fly and pests crawl, so wrapping greased or otherwised stickied paper around a tree trunk can be effective. Plants prone to fungus and water-related problems are usually pruned to maximize air flow and sunshine through the branches (see "pruning" above). Some beneficial insects eat pollen and nectar as well as pests, and are attracted by plants with shallow blossoms so the plant's food is accessible without specialized mouthparts; most plants of the Asteracae ("sunflower") or Umbelliferae family qualify (see Kourik for more info). A predator eats other insects; a parasitic insect implants an egg inside the victim: the hatchling then eats the victim from the inside out, as in love.