These tactics are shown in the alternate strategy video.
If you're using the rifle, stop shooting when you no longer have clear line of sight to conserve ammo.
Firing continuously while running to the next statue and back should use up about one clip of ammo. Release the target lock button as you wait behind the statue so Lara will reload. Then repeat the process.
If Takamoto moves, run to the statue opposite where he ends up and start the process again. Repeat this until he is dead. He will continue to fire energy blasts at Lara as she runs, but as long as you keep moving, Lara should lose very little health. (Thanks to Anton B. for this tip.)