Nitrogen, Phosphorus, and Potassium are the three main plant nutrients plants need to survive. When you buy a fertilizer they are listed by weight on the label ( Nitrogen/Phosphorus/Potassium )
Normally houseplants get good soil and repotted frequently so it is not necessary to fertilize them much, if at all, but watch for these symptoms and give your plant more nutrients if you see them.
Yellowish green leaves, oldest leaves turn first and tips and edges of leaves yellow working back toward plant. Growth is slow. Often veins remain green. This means you need more nitrogen or iron or both.
Leaves die back, older leaves and stems may turn purple, plant is slow reaching full size, plant may be stunted. These are symptoms of low phosphorus.
Leaves distort and curl under, older leaves get brown edges and drop. There is poor root growth. These are signs of low potassium in plants.
Small, narrow leaves with assorted black spots in yellow areas can indicate a zinc deficiency. Plant may also be stunted.
Overly bushy plants with crinkled and deformed leaves often want more boron, but don’t over apply.
Upward rolled young leaves want more copper or suphur. New leaves are often light green with no color variation. New leaves may be small and yellow.
In general cupping of leaves, yellowing, browning, and stunted grow indicate the plant needs a bit of fertilizer. While your house plants should need little to no fertilizer, they do need some, especially if you see any of the above traits in your plants. Pick up your favorite brand at the local store and follow the directions on the label.