Keep your forces moving and try to maintain momentum over a long distance. Concentrating on artillery rather than air power allows one to cover large spaces safely, as well as being able to attack at the other side of the map. Recon units move faster and see farther than other forces, therefore it makes sense to keep them out at front. Use the tanks in open country and keep them moving constantly. Tactical bombers should be used as flying artillery, eg. the Ju87.
Level bombers can paralyse naval forces and bomber units for the turn's duration.
They would not have a chance in the city streets. Bomb the position and move on. When the enemy line starts to break, charge the tanks through, led by a recon unit. The best way of dealing with attacking artillery is to bomb it.