"So, you want to control everything I know and love? Here's all the information you need to do that all located in a tiny and convenient manual!"
Taking Over The Planet By Force:
If there is already a player controlling it you may make a post challenging the current ruler on Fridays only. Your intentions must be clear at the start of the battle and explicitly say, "yo, muthfucka, I want yo shyt." If you fight them and win then you take the planet. If they fail to respond within a fortnight then they forfeit the challenge and you win the planet (unless the player has given a legitimate reason for being gone prior to the challenge.)
Squatter's Rights:
You may also rule a planet by getting 100 posts on the site* and gaining admin approval. This only works if there is no current ruler or if the ruler has been inactive for a long time.
Elections:
For planets with no ruler or active ruler elections will be held in the Grand Senatorium where you should make your desire to rule the planet in question known. Votes will be held and a ruler will be chosen.
Other Methods:
There are other ways to obtain a planet to rule over if these do not suit you. One way is to wish to become a ruler of a planet through the dragon balls. However, if there is a ruler you must make a wish with the Blackstar dragon balls to take their place. If there is not then any set of dragon balls will do.
Another is to simply buy a planet through the planet shop, which is unfortunately not up and running quite yet.
*100 posts on the site is a requirement to become a ruler no matter what method you use.