Capture the nearby Port and Airport and any nearby cities as soon as possible. For that I would use the Artillery to destroy the first meteor. It also helps to get rid of the other two. After/as you are capturing the cities, deploy Bikes to the other cities. Build Battleships, Rockets, and anything Anti-air to get rid of the plasma and any Seaplanes. You'll probably want some Anti-tanks, but mostly tanks etc. Bombers can be good early on but then the enemy will start building their own Anti-air. The sea shouldn't be focused on that much even though it takes up roughly 40% of the map, but take care of it early.