Assuming your doing all the things you are supposed to be doing for this plant...
consider these basic needs of all plants,
sunlight, is it getting the proper type and amount of sunlight needed for that particular plant?
soil, is it in the right kind of soil? some plants need light loamy soil while others need dense sandy soil. if you find that the soil isn't correct for that plant, replace it.
water. is it getting the right amount of water? generally speaking, if the plant looks yellow and wilty it's probably getting too much water, dry and crumbly, not enough. (be sure to read all you can on your specific
plant though. there are exceptions to these rules)
and last but most important, how do the roots look? If your plant is root bound or root rotted it won't be able to take up the nutrients vital to healthy shoots. some plants like their roots to be a little cramped however, so again, check on your plants requirements.
after this checklist I would definitely check on feeding requirements and try to do it at least annually.