move any pictures and music to the SD card first - those tend to eat up a lot of room (I use ES File explorer, but there are tons of file management apps)
non-movable apps are just that, non-movable. In your device settings, go to apps and one by one move things that you CAN move over to the SD card - but keep in mind if you have an app with a widget you use, moving that app to the SD card disables the widget. If an app is on the SD card, widgets for that app won't work - they only work if the app is on the phone's storage.
You may have more options if you root - but rooting breaks your warranty, and if you don't know what you're doing it can turn your tablet into a useless hunk of plastic - and no, I'm not kidding. ONLY ONLY ONLY root if you've done a lot of research first, have considered all the pros and cons, and are willing to take the risk. It's not an option I recommend, but it is an option.