There's a pretty low chance of accomplishing this "naturally" because the AI has a tendency to aim for Elimination or Supremacy victories and they'll declare war on you to get it. To get around this:
1. Set up a one-versus-one game against the Roving Clans. They cannot declare war.
2. Disable all victory conditions except for the Score victory.
3. Set the game speed to Fast. This means the highest scoring player wins at 150 turns.
4. Set the difficulty to Newbie so that the AI will be unlikely to outpace you in scoring.
5. It is now simply a matter of expanding to new regions, searching ruins, researching new tech, pacifying villages, and whatever else you can do to boost your score and make sure you are on top when the game runs out of turns. Ideally, grab as many regions as possible to make sure the AI can't get them. Check the scoreboard by looking in the bottom right corner of the screen at the end of every turn.
Because you'll be expanding rapidly and constantly scouting to boost your score, this method should help you unlock all the following achievements: