Besides the obvious controls on grain: paper, paper developer, enlarging equipment, etc...

There's also the personal aspect. One person's grain is another persons grainless. Print a bunch of sizes, with a variety of papers and developers, and pick what you like best. This is what is so much fun about photography.

My rule of thumb is no more than 4x by area. Thus, my max print size is 16x20. Your preferences will likely be different.