Cutting it the right way means slicing it against the grain. The grain of a tri tip runs radially from the corner opposite the crook in the meat. This means that cutting the piece in two from corner to crook and then slicing each piece it gives you the best results.
Take a look at the video below for a visual guide to cutting this delicious piece of beef.
For more on tri tip, see our post on smoking tri tip BBQ style.