The absolute best thing to do in the occurance of a tsunami is
seek higher ground as quickly as possible. if you live near the
coast, your town should have Coastal Evacuation Route signs near
every major intersection.
Get to the highest ground you can quickly. In other words climb the highest nearby hill.
When a tsunami hits, don't stop to try to take any belongings with you, they'll hold you back and then run as fast as you can away from the ocean to higher ground. If you see waves you're too close. Make sure you're always prepared for tsunamis if you live close by the ocean and especially if one has hit there before.
Basically, you want to get to the highest ground you can reach quickly. The idea is to get above the level that the water may rise to. That can sometimes be in a building, but you do NOT want to trust a building that is likely to be swept away itself. You are much better off climbing the nearest hill.