How do I tell what type of food to feed plants, i.e. which plants like which types of plant food?

This question needs a different answer for different people. A commercial nursery or flower producer must keep very tight control over plant nutrition in order to grow plants efficiently and of a quality that will satisfy the buyer. This involves soil and tissue testing and, in some cases, day by day manipulation of the nutrients supplied. For the gardner, the pressure is much less and almost any fertilizer in small amounts at regular intervals will keep plants growing. For the homeowner with some houseplants, the approach is even more simple. For the most part there is no need to get a lot of increase in size from the plant, so all that is required is a very small quantity to maintain the plants day to day activities. I would suggest one of the national brands, used at about half the recommended dose on the package through the summer months, and no feeding at all through the winter. Try the simplest answer first, and results will be good in most cases, and don't worry about the various packagings that the fertilizer people use - they are mostly to sell more product. Derek