Problems with houseplants may take trial and error to overcome because one symptom might have several possible causes. Understanding signs of plant stress, along with possible reasons for the trouble, will allow you to change your approach to care until you solve the problem. It's also helpful to understand the different micro-environments in your house---the humid rooms versus the dry rooms, for instance. Lastly, educate yourself about each particular plant you own. Start by keeping the instruction tag that comes with the plant.
Too Much Light
Plants that receive too much light wilt, or the leaves begin to shrivel and/or turn brown. Plants do need some darkness, though the amount will depend on the kind of plant.
Too Little Light
Without enough light, plants make small and/or pale leaves, fail to bloom or become leggy. Leggy plants have a lot of stem between leaves. Lower leaves may begin to fall off. Move the plants to a sunnier spot or add artificial light. South-facing windows receive the most light, followed by west-facing, east-facing, then north-facing windows. Regular light bulbs do supplement natural light, especially special fluorescent plant bulbs.
Plants need oxygen in their soil or they drown. Signs of overwatering include soft stems at the base of the plant and root rot (soft, dead, dark roots). Plants in plastic pots need less watering than clay pots, which absorb water. Learn the watering needs of your plant.
If your plant fails to grow and begins to turn brown and die, it might be that you aren't watering it enough. Check the soil. If it's hard and dry, you've waited too long.
Other Water Problems
Treated indoor water might contain salts or chlorine, which plants don't like. If you suspect your water might be bothering your plants, try using untreated water, say from your hose, or letting water sit a couple days so that chlorine evaporates. Untreated water may be very hard, containing too many minerals for some plants. In that case, you'll have to treat the water or buy water. Use room temperature or warm (not hot) water on plants so you don't shock them.
A potbound plant has roots that have outgrown the pot. Roots may come out of the drainage hole or even break a pot. Use a larger container.
Holes in leaves, webs and other signs of infestation should spur you to action. Immediately quarantine the plant and check others for pests. If the plant is heavily infested, you might have to throw it out. Some pests can be dislodged by putting the plant in the shower. Another method of ridding a plant of pests is to cover the soil with plastic wrap before dipping a plant in a very mild solution of water and bleach, or water and detergent. The plant might be better served by rubbing leaves with alcohol or plucking pests off. The method is determined by the type of plant. Most methods risk damage to the plant. The first step to pest control is to use potting soil, which has been sterilized, and not garden soil.
Indoor environments might be too dry for some plants, such as ferns. If you need to add humidity, you can mist plants that don't have hairy leaves. Another solution is to put the pots of indoor plants on a tray that has been filled with pebbles. Add water up to the level of the pebbles and, as the water evaporates, humidity around your plant increases. Keeping plants in groups also raises humidity. You can also put a small pot in a large one, filling the space between pots with moist peat moss.
Use fertilizer that is made for houseplants. If you're not sure how often you should feed your plant, follow the directions on the fertilizer. Signs a plant needs nutrients are little or no growth, yellow, spotted or pale leaves, and failure to bloom. Too much fertilizer will cause leggy growth and burnt looking leaves.
Plants don't like shocks and extremes. Avoid putting houseplants near heat and cooling ducts, near a stove or in a drafty area.