I’m always surprised at the reaction I get from junior designers every time I teach them how to justify text. Their reaction is always the same: “I did not know that a justified text could look so good. Why don’t they teach that in school.”
The first thing you want to do is disable all the functions programmed into your software that track type for you. Remember, you are the type-setter not the software. For example, in Adobe® InDesign® or Illustrator® choose ‘Adobe single-line composer’ in the paragraph settings, not ‘Adobe every-line composer’.
Next flush left all your text and follow instructions given above on how to typeset a good flush left, rag right text.
Once your text is perfectly typeset flush left, simply select ‘justify’ and voilà magic! If your rag right was nice and tight and you used hyphens in the correct places, your text should not have moved and be perfectly justified. If it did move on a line, simply force it into place manually with a soft return. For a more professional look I personally like to hang hyphens, quotation marks, commas, period, asterix, etc.