For this you first have to find the sensitivity right for you. I start the game getting through wave 9 w/o losing a city and at the beginning of wave 10 I shot about 7 or 8 missiles from right to left using my left turret at the beginning of the each wave across the very top almost and would get the first wave of missiles gone. After the left to right I would go right to left with my right turret for the next wave. This is the most effective way to keep your cities alive I thought. For any missiles that get by use your center turret to take them out. To deal with the smart bombs you either have to nail it right on the dot or as it's coming down lay two missiles a little apart from each other on both sides of the smart bomb and let it die and finish the next wave of missiles as it comes. Kill the spaceships asap after your shooting from right to left with your turret (if you use this method.) It will take some time to figure out where to strafe on your screen, but practice makes you better.