This is not like a normal house plant (see how an orchid grows), so there are a few simple things to do so that your plant will be healthy from day one.
To be safe...no direct sun should hit the plant! Bright indirect "reading the newspaper at the kitchen table" light is good--You can/should move the plant into dimmer conditions when it is in bloom. Don't put it by the air conditioner vent.
Water when the potting mix is nearly dry, but don't let it dry out completely/crispy for more than a day or two, and do not keep it wet by watering a little every day. It is best to determine how many days it takes for the plant to dry out and then schedule to water then.
You can take a Phal out of the pot and set it bare root on the kitchen table for two days or so and the plant would not blink, so do not be afraid of letting the pot dry out completely for a couple of days. Consistently watering one or two days after you think you should water is a good rule of thumb, but don't let the pot go dry for 4-5 days or the plant will get floppy.
Water well when you do water..run it under the sink for at least a minute. This flushes out old fertilizer salts.
The biggest danger with Phals is what you do with them in the first few days. The plant will most likely either be over watered or underwatered in the store. Over watering causes root rot and is the single most common cause of plant death for beginners.
Here is the way I get around the problem. I soak the new plant in distilled water for a half hour right when I get it home. If the plant was dehydrated, this helps, and if the plant was waterlogged, this doesn't change anything except to flush out some toxins. Distilled water will be easily taken up by the plant, and will also help leach nasty stuff out of the pot better than tap water (which can have a high pH, and not do so well with stressed roots).
Drain the pot and tilt it little on an old towel to pull out any excess water.
Put the pot on top of something (two pencils, baking rack etc) that will allow a lot of air to get to the drain holes under the pot. Do not worry about humidity trays, or misting the plant for now.
Let the plant sit, and each day lift it up to see how dry it is. Look at the holes in the bottom and see if the medium is still moist there. Chances are your plant will come in a plastic pot. When the top of the plant is heavier than the bottom you know it is drying out. A 4 inch plastic pot may be ready for another watering in a week, sometimes up to two weeks, sometimes less than a week.
If you look at the holes in the bottom, and the bark is dry, the bark in the middle of the pot is usually still damp for a couple of days.
You will probably have to put the plastic pot inside of a clay pot so that it doesn't tip over.
in conclusion:
-Put it in comfortable indirect light.
-Water well and let dry out well when you get it home.
-Water on a schedule that ideally lets the pot be nearly completely dry for a day or two at most (approx. weekly in the summer, every 10-14 days more or less in the winter).
FOLLOW UP: for other types of orchids
The most common types of orchids (by number of plants) I see in the Local Home Depots, Lowes, Trader Joe's etc, (those orchids most likely to be a first time impulse buy) are Phalaenopsis hybrids, hard cane Dendrobium hybrids (Dendrobium phalaenopsis types), Oncidium Gower Ramsey (a yellow dancing lady), Oncidium Sharry Baby (a red and white dancing lady, smells like chocolate), Colmanara Wildcat (star shaped flowers mottled with earth tones), Cattleya hybrids, and Miltonia hybrids (flowers resemble those of Panseys).
Of these, the Dendrobiums, Oncidium Sharry Baby, and the Cattleyas eventually need higher light levels in order to flower. Because your plants have been either crated up, or in a dim store for quite a while, if you try to put them into their optimal light conditions, you will sun burn them within 2-3 days. Plants are very much like people. It takes a while for them to "build up a tan" as it were so that their leaf cells do not get damaged by the solar radiation. It takes at a minimum two weeks for a plant's cells to manufacture and build up levels of the molecules needed to deal with the radiation. This is first seen as a protective red flush on lighter parts of the Phal's leaves, later, the plant will either add or remove chlorophyll in the leaf tissue and adjust molecular pathways within the leaf. When the plant has adapted, the red flush may dissipate.
The Phalaenopsis is usually considered a low light orchid because it will bloom under relatively shady conditions, but it will adapt to the medium light levels enjoyed by the remainder of the orchids I have listed. The only difference being that the others can take a few hours of direct "dawn" or "sunset" sunlight that my cause burning of the Phal's thick heat retentive leaves.
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So after your orchid has had time to adjust to its new home (2-3 weeks in moderate room light), it is time to increase light levels a little. Look around your growing area and pick out about four different light levels. That at which the plant has been for two weeks (lowest), the brightest area, and two areas in between. Move the plant to the next higher level and let it sit for two to three weeks to adjust befor moving it again. In general the other types of orchids will not show the red flush that the Phals do. Cattleyas do get a red or purple flush, the others will get a lighter green color and may get black dots "freckles" on the leaves.