My main strategy is to spend most of my time at max altitude, only dropping down to dodge the occasional missiles. Until the train tracks! Then I dive up and down repeatedly while bombing the ever loving bejeezus out of the tracks. Each segment is worth 100 points, I think. Then when you get to the part with the train engines you need to make a point to hit them because they're a pretty high value target. You end up with a lower point to hit ratio this way, but I always go by the end total score anyway.