Perhaps you went on vacation and forgot to have someone water your plants. Perhaps your plant needs better soil. Regardless of how your plant got sick, it's on its last roots--unless you do something, the plant will die. No troubleshooting guide can guarantee that your plant will survive, but a few steps may give your plants a second chance. With some investigating, basic gardening tools and patience, you may be able to save the plants from the trash bin.
Inspect the plant and soil physically. Look for signs of why the plant isn't doing well, such as extremely dry soil or powdery mildew on the leaves.
Prune and remove all dead branches or leaves or leaves and branches that clearly will not revive. If the branches and leaves are alive but too sick to rejuvenate, they will only drain energy from the plant until they fully die. Dead branches and leaves make it harder to care for the living sections of the plant properly.
Push your finger into the soil or try to pull the plant--gently--from its pot. Water the plant if you cannot push your finger in at all, if the soil feels absolutely dry to the touch, or if the plant slips easily from the container--these are signs of a lack of moisture. Refrain from watering if your finger slides in easily and the soil feels wet.
Adjust the light exposure to the plant by changing the location of the plant. All plants require some sun to live because they use sunlight to manufacturer food through photosynthesis. However, too much sun literally can burn some plants, and some plants need full sun to go through photosynthesis properly and get enough food. Use a plant lamp to increase sunlight if you suspect lack of light is an issue.
Wash the plant with plain water from a spray bottle and a soft, non-abrasive cloth. Plants have openings called stomata on their leaves; they use the stomata to breathe. If the stomata are clogged with residue and dirt from the environment, the plant may suffocate.
Talk to the plant. No, the plant won't understand you, but the plant will benefit from the carbon dioxide you breathe out during speech.
Remove the plant--soil and all--from the original container. If the roots are extending out the drain holes in the container, or if the roots wrap continuously around the root ball, the plant is pot bound and needs a bigger container. Loosen the roots from the root ball and re-pot the plant. Use a container no more than 2 inches larger than the original container; anything larger and the extra space may shock the plant.
Apply a fungicide or herbicide to battle mildews, molds and bugs that may be hurting the plant.
Fertilize the plant. Plants in containers eventually will use up all the nutrients in the soil in the pot, leading to deficiencies in the plant. PH levels also may be off, depending on how much you have fertilized, the type of soil you used and how much matter has decomposed back into the soil. Fertilizing often fixes these problems. Do not fertilize your plants until one month has passed after re-potting, however, as the plant will be shocked enough from getting into new soil.