Place African Violets in an east, west or north window, unless you are in the north and then a southern window in the winter is needed for blooming. See how, in one picture, the leaves are upright instead of laying flat? That is how African Violets respond when they are receiving too little light. If yours do that, give them more light.
The consensus is that African Violets soil must be kept moist. But I find mine do best when I thoroughly soak them, then let the top half inch or so of soil dry out. Many people use wicks to water them, or place them in a saucer and water them from the bottom only. The leaves do not like cold water or to be wet for any length of time, brown spots will occur where cold water hits them. If the pot is clay, the leaves that rest on the edge of the clay pot will die, however the plant itself will be fine.
African Violets actually like smaller pots than these are in currently. The pot should be one third of the diameter of the crown of the plant. They are in flower about nine months of the year provided they have enough sunlight. African Violets can get as large as 9″ in diameter.
African Violets do not like to be cold. Keep them above 60′ F and use warm water to water them.
It is very easy to propagate African Violets. Cut off a leave and leave the stem as long as you can. Put the stem in water or very damp soil. Make sure the leave part is not touching the water, prop it up with toothpicks if need be. When you see new growth treat it as you do your other violets.
If new leaves are stunted and curled you likely have cyclamen mites. Usually you can not save the plant, only take it away so as to not infect your other plants. You might try an insecticide.
African violets from space