Depending on the condition of the brick. As long as there is not any spalling peeling brick, I would use some TSP,water and a good stiff Broom/brush.
Then wash it down with some water.
Never sandblast, or High power wash. The powerwash can be done with a wide stream and a low PSI washer., However it may leave streaks where the wand gets to close, and you can damage the brick.
Good old fashioned elbow grease is your best bet.