I believe most victims of Tsunami are killed by either being thrown against something during the initial impact, or being dragged away by the backwash currents. High Ground is the obvious, and probably most effective solution.
It's over Tsunami,
I have the high ground!YOU UNDERESTIMATE MY POWERDon't try it...

Actually, the
safest place to be during a tsunami is in the water, sufficiently far from the shallow coast waters. When the wave hits shallow water, the energy of the wave motion conserves (reasonably well), but due to reduction in the water depth the surface amplitude increases immensely. If you're far enough out that you're not washed to the shore and then back with the receding water, hitting stuff like trees, buildings and cars on the way, you should be just fine.
On the other hand if you're actually on the beach and see the wave coming, the safest bet is to either get on top of a solid building and hope it doesn't collapse under you...
Of course, there are different kinds of tsunamis, depending on how they are originated. The phase of the wave front hitting the coast line is pretty important. Waves with negative initial amplitude have a "deeper" area ahead of them, and they give the warning with fast receding waters. Positive initial amplitude waveform means the water rises immediately with no further warning.
By the way if you go to area with possibility of tsunamis, make yourself familiar with paths to tsunami shelters and in general instructions for such incident. That's going to increase your odds of survival much more than asking about it from internet people.