Start with an orchid suited for the light, temperature, and humidity where you will keep it. Always buy from a reputable nursery, and never purchase plants potted in soil because potting orchids in soil leads to root rot.
Prepackaged potting mix, or Martha's recipe of equal parts fine fir bark, medium fir bark, and charcoal
Repotting Orchids How-To
1. Choose a pot large enough to contain the plant's root mass with an additional inch of space across the diameter. Before repotting, water the orchid well so its roots will be more pliable. Carefully remove the old potting mix from the roots, and trim any dead or damaged roots with a sharp, sterilized razor blade or scissors.
2. Set the plant at the same depth as it was in the pot you bought it in. Add new potting mix to the pot, just up to the bottom of the root mass. Then add potting mix around the root mass, tamping gently. When the pot is full, tamp it several times on a hard surface to settle. Some mediums, such as sphagnum moss or pumice stone, must be arranged around the roots, rather than sprinkled into the pot. Wear gloves, and use care while arranging this type of medium. Secure the orchid with a stake to keep it from wobbling.
3. Set the orchid in a sink, and pour cool (50 degrees to 75 degrees) water over the top, avoiding blooms. Flood the plant until the water runs out of the bottom of the pot; allow it to drain.
Orchids prefer humid environments, so protect your orchid from the drying effects of radiators and air conditioners. Place the plant in an area that has a humidity level of at least 50 percent. You can ensure a humid environment for your orchids by grouping them in a tray of pebbles and water. Make sure that the pot sits on top of the pebbles, above the water; if the pot sits in the water, the orchid's roots will rot. Water the plant according to the needs of the individual species.