Since you might not have much (or any) warning, preparing for a tsunami is a bit like preparing for an earthquake. You have to have your disaster supplies ready. Build or purchase a disaster kit. Have a communication plan.
Planning is key. Know where you will go and where you will shelter in the event of a tsunami — make sure it’s somewhere uphill and as far inland as possible, away from the coast. Your community might have predetermined evacuation routes. If so, know the routes and the alternatives in case the routes get jammed with cars.
How far are you above sea level? You should know how far you have to evacuate to be out of the way of the water. To be safe, you should be at least 100 feet above sea level or one mile away when the first wave hits. Unfortunately, it’s not that simple and even being 100 feet up won’t guarantee survival. So don’t stop at 100 feet if you can help it.