Fable III

To access the road to rule at any point go to the portal in the main room of the sanctuary and hold A. To get this achievement you must open all 48 chests. The chests will continue to become accessible as you gain supporters and all will be available when you become king. The chests will cost you anywhere from 2 guild seals to 100 and you need slightly more than 1400 seals in total for the achievement.

To gain guild seals I recommend following the main questline and doing any side quests that pop up along the way. You also get seals from combat and can upgrade legendary weapons to increase the rate at which you receive them. Also joining another players game nets you seals at a very fast rate when they are doing the main storyline.

*SPOILER*

After you have beat the darkness and saved the land, everytime you rub up to someone you will receive approximitely 1 guild seal.

just to add another method, which i discovered while trying to get the 20 friends achievement ( :@ ) if you have a character who, or you know someone who has finished the game and has a high charisma dog, ask them to join your game and interact with people in your towns, you get 6-10 seals for each one.
my second character had only just reached brightwall and the character that joined was a maxxed up king. i had 300+ seals just by having the king dance with everyone in town. (still no 20 friends achievement though :/ )
i recommend doing this as early as possible as i believe you get more the earlier you are, so make sure you farm the dweller camp entirely as well. (might even work as early as the castle but i didnt join that early)

hope this helps.

Just a slight correction (with respect to the previous *SPOILER* solution from Clubmau5, fantastic might I add):

Notwithstanding what I'm about too point out, you won't gain guild seals by rubbing up against any random NPC villager.

The villager must first consider you to be their "Best Friend."

This is most easily, and thoroughly, accomplished by simply proving to the world that you are a successful and compassionate leader...

*SPOILER*

In doing so you must select the most "pure" options, or those which are considered "good' during your royal appointments. For instance, building an orphanage rather than a brothel, a school instead of a child labor orientated factory, or simply investing personal funds into your royal treasury. This may make your play-through more challenging (if you intend on portraying yourself as a righteous leader, that is), however, it is well worth the effort if you intend on obtaining this particular achievement ASAP.