What is the best way to adjust justified text(see image) so that it looks aesthatically pleasing. What is the best practice when adjusting the values in the justification settings?
The most readable English text is short lines of left justified, high contrast, sentence case, modern serif, properly kerned and leaded, 12pt or larger, short common words.
It goes down hill from there.
As far as looking nice, well that's a more complex answer, and highly subjective. It depends on what you like and what you're trying to convey and to whom.
I would always choose readability over style, and when it comes to style I consider it successful when the reader does not notice the font styling at all, they just get the message from the writing that you want them to.
Justification is usually about the end product. You would find it difficult to read a newspaper that was justified left. Newspapers and magazines will have text columns justified left & right for readability. Books often are the same, but not always. A blog, shot story, or letter are fine justified left. I've worked for both large newspapers and magazines.