NOTE: you can install a few alternative icons themes directly from the debian repos by installing the libreoffice-style-* packages.
Anyway, we're commiting sacriledge by making our libreoffice look like MS office. You can obviously use the instructions here to pick a less controversial look.
First go to http://charliecnr.deviantart.com/art/Office-2013-theme-for-LibreOffice-512127527 or use wget:
wget http://orig11.deviantart.net/e10d/f/2015/059/7/3/office_2013_theme_for_libreoffice_by_charliecnr-d8gwo4n.zip mv office_2013_theme_for_libreoffice_by_charliecnr-d8gwo4n.zip images_office2013.zip sudo mv images_office2013.zip /usr/lib/libreoffice/share/config/
Then in libreoffice go to Tools/Options/Libreoffice:view and pick your theme:
This is a weird one. Go to Tools/Options/Libreoffice:personalisation and under Firefox themes select own theme, and Visit Firefox Themes.
Then paste the URL of the theme you want. I used this URL: https://addons.mozilla.org/en-US/firefox/addon/office2010-edit/
And this is how libreoffice writer looks now: