The safest way to use a rotary blade is standing up at your cutting table. You need to be able to look straight down to ensure that your blade is firmly placed against the ruler. Leaning forward from a sitting position is not as steady and could lead to crooked cuts or a slice into the hand holding your ruler steady.
Be sure to keep a supply of spare rotary blades on hand. Trying to cut with a nicked or dull blade will lead to nothing but frustration. You may also be tempted to press too hard and have the blade slip and cause an injury.
Take the time to doublecheck each piece of fabric as it is added to your foundation. Cut a large chunk of fabric to be sure that your seam allowances will completely covered after the piece is flipped to the right side.