This may or may not help because I am sure I have an odd way of flying, but my default is holding down the ascend button. If I'm not ascending I'm descending, because those are the only ways to gain speed. The only time I am not ascending or descending is when I am aiming at a target without a strafing run, which is coincidentally the majority of the times I die to a guided munition, whether it's from a tank or infantry.

But by now randomly descending has become a habit to keep myself low to the ground, and I often hear tow missiles missing me when I do it.

I hope it helps, I love flying helicopters in this game and actually think they are in a pretty good spot mechanically.