Measure the surface of the brass with a tape measure so you know how much room you have to stamp. Place a number or letter punch side-by-side for each letter or number you want to stamp on the brass. Measure the width of the punches with the tape measure. If the punches will not fit, look for ways to abbreviate the stamp, or consider two rows.
Place a ruler on the surface of the brass and draw a straight line with a marking pen. Alternatively, place a strip of tape across the face of the brass to give a straight line. If you have a straight line on the brass, you can use that line to position each punch in a straight line. After the first punch, do not move it until you place the second punch butted against the first punch. If you do this as you place each punch, you will have a straight line and equal spacing. This provides a professional look to your stamping.
Place the brass onto a solid surface that will withstand moderate hammering. Do not attempt to hold the brass and punch in one hand and hammer with the other. This will result in poor stamping. Use a good claw hammer or a weighted brass hammer. A weighted hammer increases your ability to strike the number or letter with one blow instead of multiple blows. Striking the number or letter in one blow means you do not have to attempt to place the punch back into the exact same location for a second attempt.
Hold the number or letter punch as perpendicular to the brass surface as you can. This will help you strike an even blow with the hammer. If you have the punch at an angle, one end of the letter will dig deeper into the brass than the other end. Be careful that the punch does not shoot out when you strike it. This could scratch the surface of the brass and create damage.