To trim spurs, you will need a small, fine toothed, hacksaw, or a small rotary cut off wheel. You can trim spurs at any time, but some prefer to do it when the moon is full, so the blood will be in the head of the bird, to help keep any bleeding to a minimum. Spurs have a core, and an outer husk. The core is usually about 3 times as long as the diameter of the base of the spur. To avoid cutting into the core, and getting some bleeding, cut the spur off past where the core ends. For most adult birds, this will be about 5/8 of an inch from the base of the spur.
Begin by wrapping up the bird in an old towel. Hold the spur by where the spur connects to the leg. It is important to not just hold on to the leg, you need to hold the spur too. Use your saw to cut the end of the spur off in the location I discussed earlier. Take care if you are using a hacksaw, to not let the saw grab hard, or you may hurt the bird. I like to use very light pressure, and short strokes. If you cut them off with a rotary tool, take care not to accidentally nick the bird anywhere, as this tool will cut anything it touches. Some prefer to use the rotary tool, because it creates heat as it cuts, and thus cauterizes the wound at the same time. If you cut them off at the right location, you won't get any bleeding at all. If you do nick the inner core, don't worry, it will bleed some, but will heal fine. Step by step pictures of this procedure.