The good news is that almost every developer will work with nearly every film. The bad news is that it will take a lifetime in the darkroom to try every combination. Sooner or later one will realize that manufacturers know what they are talking about and writing down on those small pieces of paper that come free with their products. They know what works best... if your results do not come up to scratch, there must be something wrong with your technique rather than the manufacturer's researches, descriptions and final instructions.

Eliminate the variables
Because there are so many variables in photography it's best to eliminate as many of them as possible. By constantly changing films and developers more variables are introduced. But finding the right combination and refining it through practice does at least enable you to produce predictable results.

Conventional photography is based on silver-gelatin films. The grains of silver salts are relatively small in slow films and larger in faster films. If you make exposures in bright light with slow-speed film you will see a smooth tonal gradation in the processed film. If you make exposures in low light with fast-speed film your results will usually be more grainy.

There are different reasons why grain in a print should or should not be visible. Some photographers and critical viewers dislike seeing it... for others it is the essence of the medium. There are instances when it is valid... and subjects for which it is generally unacceptable. However, you should be practiced enough to produce photographs under extreme conditions of lighting from good to bad, with guaranteed results. That is why it's advisable to have two good film and developer combinations in your armory.

Classic combinations
Two combinations I first used 25 or so years ago are Ilford FP4 in ID-11 diluted 1+1, and the same company's HP5 (or was it HP4 then?) in ID-11 undiluted stock solution. I have tried many other combinations since then but usually come back to these two basic "classics" for their known effects and for the results I want.

Ilford's ID-11 has to be mixed-up from a two-part powder pack. I use commercial bottled water (Volvic... always on hand as I drink it a lot) for all powdered developers because it is better than filtered tap-water in consistency. Before use I take the "strong edge" off the freshly mixed 2.5 liters of developer by adding half a liter of the old developer stock solution to the fresh mixture.