# what was right in the eyes of Yahweh

"the things that Yahweh said were right" or "the things that Yahweh considers right". See 2 Chronicles 14:2. 

# walked in the ways of David his ancestor

"lived the way David his ancestor had lived" or "followed the example of David his ancestor" 

# did not turn away either to the right or to the left

"did not do anything that would displease Yahweh" or "fully obeyed the laws of Yahweh"