I am using Inkscape 0.91 on a windows 10 (and windows Vista) platform and each time I restart Inkscape, I must reset my preferences for fills, etc. for the different shapes. I would like to be able to use my preferred settings (preferences) on all new documents. I thought this should be rather easy, but this does not seem to be the case. How can I accomplish this?

@virsto:

I'm also running Inkscape 0.91 on Windows 10. I recently started a project which will have many SVG files so I created a new default.svg to use for the whole project

Your Personal Inkscape files reside @ %Home%/AppData/Roaming/Inkscape/templates
the Inkscape default page can be found @ %Inkscape_Install_Path%/share/templates

Make a back up copy of the existing default.svg file and rename it to default_orig.svg
save that file in your personal templates folder - I only speak and read English, so I didn't worry about the translation files

Open Inkscape and you should see the normal new page file where you need to do all your modifications again

this time, setup your page the way you want it then before you do anything else click File->Save a Copy ...
save the page into your personal templates folder as default.svg

Close out of Inkscape completely

Open Inkscape again, and it should load your default.svg file instead of the installation default
Check your settings to confirm that this time your customizations have been retained

now you should be able to work without the need to reset each new page

The tools' preferences can be set by double-clicking on the respective tool's icon. There you can choose if you'd like to use the 'last used style' or a specific style for the current tool.

Here's a tutorial, in case you might need it: Customize Your Inkscape Tools' Styles
(It was written for super newbies, so apologies if it seems over-simplified.)