By grinding spices, you are keeping the spice whole until it is needed to be used for cooking, which helps retain essential oils. This improves the flavor and strength of these spices immensely. It can also be far cheaper than buying pre-ground spices from the supermarket.
Roasting will help bring out the oils in the spice. Put the spices in a hot pan and shake it occasionally. Roasting time varies, but doneness is determined the same way: The spices will have a flavorful but not burnt scent. Mustard seeds will pop when they are done.
You have a choice of instruments to grind your spice:
Mortar and pestle
A more expensive mortar and pestle isn't necessarily better, just fancier looking. Molcajetes and Thai stone mortars have a rough surface that will make grinding faster. Put the spice in the mortar, stir with the pestle, and knock the spice back to the center occasionally.
This needs to be a separate device from the one you use to grind coffee: no matter how well you clean, your coffee will pick up spice flavors. A blade grinder will be easier to control than a burr grinder, and a stainless steel bowl won't pick up flavors as readily as a plastic one.
Large spices like nutmeg will be hard to grind by hand, but you can use a fine grater. You can buy a "nutmeg grater," but a microplane will do a much better job of getting the spice from the seed to your dish and can be used for other things like zesting oranges.
A pepper grinder will only grind pepper. Unlike other spices, pepper does not need to be roasted. Look for a model that has a stout body and a large opening to pour in peppercorns. Motorized models will wear out faster than hand grinders. If you don't have a lot of arm strength, get a lever-action grinder.
Posted 3859 day ago