In order to flourish, many species need differences in temperature between the day and night (a difference of some 10ēC). Inside the house you can achieve this change in temperature by opening the windows at night for fresh air.
In general, orchids need high environmental humidity. The dry air of houses, accentuated by heating, is rather compromising. You should daily air out the place where the orchids are, always avoiding cold drafts which may make them lose their buds.
Watering the plant is key. The frequency of this depends on many factors like the species of the plant, the type of soil, the temperature, light, ventilation, etc. For example, higher temperatures and more light demand more water.
As a general rule, orchids tolerate the lack of water better than its excess. Check that there isn't standing water as it will kill the roots. They sell fertilizers especially designed for growing orchids, which usually work well.
You can also use the fertilizer recommended for house plants, but using half the dose that the container indicates. Keep in mind that orchids need little food and an excess of fertilizer could burn and even kill them.
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