Adequate light is important for good growth and bloom. Plants may survive in inadequate light, but will grow more slowly and not bloom well. Any window that has strong, bright, light is good. Try to provide bright light, but not hot sun. Which window provides this will depend upon climate, season, and your particular home. Use plants more tolerant of very bright sun, like hoya and nematanthus, to shade less tolerant plants. Grown under florescent light, plants may constantly bloom. Place a two-tube fixture about 12-18" above plants, and keep on about 12-13 hours a day.
Use room-temperature water, watering when the soil suface is "dry to the touch". Plants such as streptocarpus, petrocosmea, and chirita, don't like to be constantly wet. Avoid letting thin-leaved plants, like begonias wilt. Plants may be watered from the top, from the bottom, or by using wicks or other "constant" watering methods.
Each watering, using a fertilizer with a "balanced" formula having relatively equal amounts of nitrogen, phosphorus, and potassium (the three numbers on the label are approximately the same). "Bloom boosting" formulas aren't necessary and deprive your plants of needed nitrogen.
Most African violets and gesneriads will thrive in the same conditions in which you are comfortable--not too hot nor too cold, with moderate humidity. Ideally, this means between 60 and 80f degrees, though most will tolerate more extreme temperatures. Streptocarpus, chirita, and petrocosmea will tolerate even lower temperatures and will be happy on a cold windowsill, while this should be avoided for episcia, which thrive in warm, humid, conditions. Hoya, and many gesneriads like columnea and nematanthus, will bloom even better following periods of cooler temperatures.
Use a peat-based, "soil-less" mix, consisting of at least 30-50% vermiculite and/or perlite. "Violet" soils are not necessarily good for violets! Go by the ingredients, not the label! A bag of good soil should feel like a nice, fluffy, soft, pillow. Add more perlite to soil the wetter you plant on keeping the plant. If wick-watering, using "violet pots", or other self-watering method, you must use a mix containing at least 50% perlite!
Except for trailing (and some species) varieties, do not allow extra crowns, or "suckers" to form on violets. This will only spoil that natural, flat, round appearance of the plant, and prevent it from blooming to its full potential. Most violets look and bloom best with about 3-4 rows of leaves. Most other generiads can be grown with multiple crowns and more leaves.
To keep their appearance tidy and encourage blooming, don't allow excessive growth of stolons on episcia and alsobia. Occasional pruning of spreading plants like codonanthus, columnea, aeschynanthus, nematanthus, and other gesneriads suitable for baskets, will make for a "fuller" looking plant. When kohleria get too tall or leggy, cut them back and let them branch out for a fuller look. When sinningias get old or unsightly, cut them back, leaving just a bit of stem or pair of leaves above soil level--the tuber will then produce new growth. Trim brown edges on leaves of plants like streptocarpus. Remove spent blooms and old, yellowed, or unhealthy leaves. Never remove old flower bracts on hoya, since it will rebloom from the same bract. Remember, a clean plant is more likely to be pest and disease-free, as well.
If receiving a standard African violet, pot into a 4" pot when it begins to bloom or about 6 months after the date on the pot label. Miniature violets can remain in their small pots. Most plants will need repotting every 6 months. Use a pot no larger than 4 or 5" for standard violets, and no larger than 2 1/2" for miniatures. Avoid deep pots. For other, especially spreading, plants, pot into larger pots only as root growth necessitates.
When repotting violets, eliminate the stem, or "neck", that appears above the soil by removing some soil from bottom of root ball, lowering the plant in the pot, then adding fresh soil at the top, covering the bare stem. Other fast-growing plants that can develop longer stems, like episcia or kohleria, can be treated in the same way. For all plants, never use pots significantly larger than their root system--this can lead to over-watering and root-rot.
Use very light rooting media, consisting mostly of perlite and/or vermiculite. For violets, cut the leaf stem at 1/2" and push down into moistened mix. For streptocarpus, remove midrib from leaf and firmly insert two halves (center side) down into media, like "slices of bread in a toaster". Root tip cuttings of vining, shrub-like, plants, or upright-growing plants. Root either tips, wedges, or leaves, of begonias. Enclose cuttings in a clear, plastic bag or covered container until well-rooted. Place in moderate light and pot "babies" when they are large enough for you to confidently handle.