The debian packages do not work well. Use NVidia Drivers from: http://www.nvidia.de/object/unix-de.html

Uninstall all other Drivers:

apt remove --purge nvidia-*

For older cards, you need older drivers! 304.135 OR Version 340.102 - depending on the series (check lspci)

If the module cannot be compiled, because of gcc version mismatches, install the correct version and set this one as default:

update-alternatives --config gcc # complains about missing alternatives. So install them:
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 10
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-6 20
update-alternatives --config gcc # should work now

In case the xserver still doesn't start, make sure nouveau drivers are uninstalled and blacklist them:

mcedit /etc/modprobe.d/blacklist-nouveau.conf
 
blacklist nouveau
blacklist lbm-nouveau
options nouveau modeset=0
alias nouveau off
alias lbm-nouveau off