I like line spacing of 1.2, which also happens to be the default in Kindle ebooks.
You might also pad a bit between paragraphs. You can see this in most Big Five books, at least on some pages where the book designer is evening out the display on the left- and right-hand pages.
I do this in OpenOffice Writer, whose menus are more intuitive and whose PDF output is more trustworthy than Word's. Between hyphenating, tracking, and adjusting line width, properly formatting and proofing a print edition takes a week or more. Never forget that you are competing against professionals who spending a year making a typical book ready for sale on publication day.
It isn't possible to give a general answer - each typeface will require different leading (the space betweeen lines), depending on how high the glyphs (characters) are for each fontsize.
Best thing to do is copy a couple of paragraphs in your chosen font into another document, and then try out different leading values. 1.15 is a good place to start, do one paragraph in that leading, then copy the para and try 1.05 and again for 1.25, then print out and see what you think. Give the printout to a few people and get some feedback and fine-tune.
A quick look at the Wikipedia page on leading is worthwhile because these things aren't hard to understand, but can make a massive difference to readers' experience (and therefore future sales!) https://en.wikipedia.org/wiki/Leading#Issues
A forum community dedicated to Amazon Kindle owners, authors, and enthusiasts. Come join the discussion about publishing, audio, troubleshooting, models, styles, reviews, accessories, classifieds, and more!