[Quoth]

In LibraOffice Writer:
Select regular expressions in Search & replace
\t finds tabs. Replace with a space
Unselect regular expressions
Find all two spaces and replace all with one space till none are found.
Select regular expressions and replace all with nothing for each of these "Finds":
^[ ] Remove leading spaces.
[ ]$ Remove trailing spaces.
^$ Remove Blank paragraphs.
(don't type in the Remove comments).
You can fix a lot of stuff you'd miss proofing, spell or grammar checking with a regex

The only inline formatting I use is Italics. Because there is some sort of slight bug with "character styles" when exporting (Save As) a Doc or Docx version.
Paragraph styles are fine, though again for conversions I have parent as "none". All text / paragraph styles that isn't entries in the TOC / NCX etc should have Outline Level "Text Body"
Chapter headings will normally be Level 1, or Level 2 if there are Sections/Parts at Level 1, with Insert under text flow of Page (but without a style unless it's for paper). "Text Body" styles should never Insert under Text Flow.
Indent or outdent at a first line, between paragraphs, margins and justification must all be in the style.