How to make an xorg.conf file

If you would want full and proper xorg.conf file (tested on Ubuntu 12.10):

1. Switch to console mode: Ctrl+Alt+F1

2. Kill x server:

   sudo service lightdm stop
   

3. Generate new xorg.conf file:

   sudo X -configure
   

   This will create xorg.conf.new file in your current directory.

4. Rename and move:

   sudo mv xorg.conf.new /etc/X11/xorg.conf
   

5. Return to GUI:

   sudo start lightdm
   

taken from Linux Mint forums (go to point 3. In Mint, xorg.conf is not present by default...)

For Nvidia based cards I suggest to install the binary driver from the repositories and then run nvidia-xconfig. It will create a fishbone with basic configuration. Similar commands for other binary drivers may exist.

If there isn't, just start by creating the file and enter your settings.

All configuration not set will X find by itself. It has a lot of heuristic, but yes, it may be hard to find the right setting keywords and values in order to tweak everything to your needs.