1. On the old machine, go to prefs > general and turn on Load preferences from a custom folder or URL.
2. Specify a folder, e.g. /tmp
3. Click prefs > general > save current settings to folder
4. Copy the resulting file, e.g., /tmp/com.googlecode.iterm2.plist to your new machine
5. On the new machine, go to prefs > general and turn on Load preferences from a custom folder or URL
6. Choose the folder that you copied your prefs file to
7. Restart iTerm2
8. Turn off prefs > general > load prefs from a custom folder.