Motion sickness arises because of a mismatch in the brain's interpretation of signals from the balance organ in the middle ear and from the eyes.
One thing that does help it is to focus the eyes on the horizon as that makes the signals they send correspond more closely to those from the middle ear. If in IMC, the attitude indicator (especially if it's a big PFD in a glass cockpit) can also be used for this.
The advice above about keeping busy also helps.
