For areas under 1,000 square feet, use a trowel that is pushable with blades measuring between 24 and 36 inches. For areas larger than 1,000 square feet, use a riding power trowel with blades between 36 and 48 inches.
Test the firmness of the set concrete before using the trowel. Step onto the area. If the imprint left by your foot is less than 1/8th inch deep, it is safe to begin molding the area with the trowel.
Use the trowel at 3/4 speed or less and keep the blades held flat at all times to produce a level surface. Overlap each pass by roughly half its length in order to provide further consistency in your operation. Use the floating or combined blades on the first pass.
Use the finishing blades on your second pass and run the trowel at its top speed with the blades set fully downward against the concrete. Continue as necessary until the finish has the characteristics you desire such as high gloss or matte.