Mount low on your helmet so your neck smooths the bumps and keep the arms short and snug with a thin pad and a tether, and if you go on-bike put it by the stem, angle past the bars, and lock down every strap and cable.
Ride relaxed with bent elbows and let your legs take the hits, then use stabilization with horizon leveling, higher frame rate, fast shutter and low ISO, and shoot higher resolution to crop and stabilize in post, easing off heavy features in low light.
