I think the difference between a good and an "unsuccessful" (I don't want to say bad) gardener is plant food. Good gardeners use it. Never was this more obvious that with houseplants. Anyway - Here's why...
Plants are about 90% organic - this is to say made up of Carbon, Hydrogen and Oxygen (C,H&O) - and 10% mineral (other elements like Nitrogen). The 'organic' bit is taken care of from Watering (the Hygrogen and Oxygen) and Photosynthesis (remember GCSE biology) - basically turning Carbon Dioxide into Sugars for energy.
So, they get the CH&O from watering and the air but they need the mineral bit just as much. These minerals come from the soil and their ongoing presence requires active biology like earth worms, death and decay, animal poo etc. If the plant is in a pot then this stuff will soon be used up and needs replacing.
Any plant in a pot will need a feed occasionally. Any feed is better than no feed. A once a year application of Growmore granules or Miracle-gro pellets is a great start. Feeding monthly is even better, then you can slightly tailor the feed to the different stages in the plants lifecycle (getting technical now, this'll come later). Ideally feed the plant a tiny amount, regularly. This is stop wasting feed through it leaching away, it stops over feeding (too much feed can actually burn young roots) and again, you can change the feed to suit the plants needs.
A little bit ti Technical stuff now - plant food comes in dozens of 'types' which are largely very similar. Most have three numbers of the packaging, often separated by hyphens (i.e 7-7-7). This denotes the percentage by weight of the three principle minerals, always in the same order Nitrogn (N) - Phosphorum (P) - Pottassium (K). Many also say "Plus TE/+TE" which is Trace Elements, these are important too but the "trace" bit is a clue!
In broad terms N (the first number) is for Foliage (green) growth, P is root growth and K for Fruit and Flowers. So at the start of the growing season a good 'P' feed will help "wake up" over wintered plants by boost ing their energy levels. P is also good for root veg all year long. N based feeding is primary as new season growth begins and plants bulk up (again N is good all year round for green plants (like grass)) and the K feed is most important when plants start to produce fruit and flowers.
There also a difference between feed types but simply put, liquid feed is instantly available to the plant and granular feeds need to break down to be absorbed. Everyone at Hortico knows this stuff so feel free to ask.