Hi, I want to believe that most of you know this already, but after watching a few speedruns of GTA IV I've found that not a lot of people are moving their vehicle mid-air if they are about to land dangerously or similar.
I've found that I can save myself from bad crashes and flips by just spinning my vehicle or rolling right or left.

Rolling:
Hold "A" to roll to the Left.
Hold "D" to roll to the Right.

Flipping:
Left Shift will make a Frontflip.
Left CTRL will make a Backflip.

Spinning:
Hold HANDBRAKE and A to spin Left.
Hold HANDBRAKE and D to spin Right.

Cars and Trucks can do Roll, Flip and Spin
Bikes can do Flip and Spin
Boats can do Flip

Something to note is that the heavier a vehicle is the slower it will Roll, Flip, Spin around.

i didnt knew that cars can flip. good to know for this 1 unique jump near jacobs cafe 🙂

thanks a lot man