Best practices and things to avoid for justification

Hi @Mateomono 
As you know, I already answered to this question in this thread: https://community.adobe.com/t5/indesign-discussions/how-to-make-body-feel-more-balanced-with-hyphenation-justified/m-p/15073565#M604374

I insist on the fact that all these settings depend on numerous criterias: among them, there is the language, the length lines, the font you have choosen and so on. And even if the settings proposed by @J E L work well for English, it is absolutely not sure it will work for German.

I won't give you any setting advices for hyphenation but these are my favorite justification for french:

• Long lines (text on a whole page):
  85 100 115
  -2 0 15
• Short lines:
  65 95 145 (sometimes 70 100 145)
  -4 -2 15 (or -2 0 15, sometimes -6 -4 15)
  99 100 100
  

Personnaly, I find that reducing the glyph scaling under 99% is a wrong idea, since it's too much visible. 

These are basic settings, and they need to be adjusted depending on the font you have choosen. 

Hi @Mateomono, congratulations designing your first book! James gives some great advice. There are so many things to learn. 

If it helps, expert Mike Witherell gave me these “tried and true” settings and I start with them:

Hyphenation: 9,3,4,1, off, off, off

Justification:
80/100/120
-5/0/5
95/100/105

(Sometimes I reset the Glyph Scaling to 100% across the board if I'm finding trouble with a book that has certain glyph characters.)

I also use this No break GREP style: .{10}$ in my paragraph styles, which is used to match any sequence of exactly 10 characters at the end of a line. You can change to 8 or whatever works better for you. Let us know how it goes and come back for any other questions you have.

From your several posts and questions, I think you are expending too much focus on this detail. Unless you have special requirements or are working within layout rules that work against text justification, you can almost certainly leave the page-by-page justification and hyphenation to the long-refined, well-implemented rules InDesign uses. If you're examining every page and finding "flaws," I suggest you look at any selection of well-published books and you will find pretty much the same level of imperfection.

Yes, you can adjust the justification tools to be optimal for a given type of content — if the material has many long words, as for technical subjects (or, if I recall for your project, German), there are better and worse settings for an overall optimal result. But there are no hard and fast rules or settings away from the well-honed rules for each language. (It is essential that you assign a correct langauge to each paragraph style, so that you aren't trying to justify/hyphenate German using English rules, and so forth.)

And in truly fussy publication, it's not unusual to make a final pass through the pages looking for faults and applying spot correction to get rid of bad breaks, stacks of hyphens, "rivers" of white space etc. The best fix for that is to have full editorial power so you can rewrite a bit, shifting or substituting words for a better flow, but just a bit of squeeze and extend here, or forcing a different hyphenation break, can do almost as much.

If this is your first book, you have many, many things to learn and apply to get a quality result. Worrying about the finest points of the justification is... way, way down the list of things to consider.