Do everything wrong! I'm joking (ok, half-joking), but since the minimization of grain has been a constant struggle for B&W film users and manufacturers since the advent of miniature film, if you simply reverse the conventional wisdom on film exposure and processing, you'll get big grain by default. There seems to be some confusion on this point in then posts above that recommend UNDER exposing your film. This is the opposite of what you want to do. Underexposure/over development is a good recipe for high contrast/ minimum shadow detail, but if one looks at a pushed negative, they almost always look watery thin, especially in the shadows, where there's almost no density. Density is made of grain, so what you want is a high density negative. You can still get a full range of tones in a high density negative, if you develop properly, but it will suffer a loss of sharpness, compromised gradation, and most of all, increased grain. You should also favor a low sulfite developer, like Rodinal, or even a print developer, suitably diluted. Delta 3200 is a low contrast film with a real emulsion speed of around EI 800-1000, so if you were to expose it at EI 400-800, and develop it to your desired contrast in a dilute print developer, You'll see a whole lot of grain. Whether or not you'll like the look of the grain is a personal matter. I personally don't care for the fluffy grain of Delta 3200, but the grain of Tri-X is so classically beautiful, it's almost irresistible. So, to summarize: overexpose, use a low sulfite film developer, or a dilute print developer, and develop to desired contrast. This last point is not as clear cut as it might seem. Over development will undoubtedly increase grain in the negative, compared with underdevelopment, but a dense, low contrast negative printed on a high grade of paper might be a grainier final product. Good luck!
Jay