What's the best thing to take for motion sickness to prevent it?

Avoidance: Avoidance is the best treatment but that can be difficult. Motion sickness is due to incongruous information from different sensory systems and some people are very susceptible to this. Avoiding or minimizng this conflct cures the symptoms. But sometimes that can't be avoided so medications like Meclizine or scopolamine are effective. Combination therapy (nausea + dizzy meds) are very helpful.

Motion sickness: Atropine-like patch used behind the ear has been proven to be very effective ( transderm scōp (transdermal scopolamine) patch is the name.