I love to run non-standard versions of games. It gives me a chance to personalize an established setting to better reflect the kinds of stories I like to tell with my players. But on a more practical level, it really broadens the spectrum of games I find myself interested in trying out. I'll confess right now that I never met a RPG I fully liked as-presented. Usually there's some small aspect of it that I wish were different, and the beauty of being the game master is, of course, you can change anything you want to suit your needs. After almost a decade of running games, I've noticed there are five general ways I tweak a game in order to make it more interesting. I invite you to try using one of these techniques as a way to experiment with a game you might otherwise not run.

From least amount of work prior to starting a campaign to most, they are:

1. Emphasize Elements You Like: Read through whatever the core book of the game or campaign setting is and note all the phrases and ideas that grab you the most. If you're into lists like I am, you may even want to prioritize yours once you're done so you know what the top handful of ideas are. Then design your campaign in order to explore those elements and ideas in-depth.

Example: In the Forgotten Realms campaign setting for Dungeons and Dragons, magic is caught up in something called the Weave. This is the most interesting aspect of the setting for me, so if I were to run a Forgotten Realms game, I would most likely make it a spellcaster-focused campaign in order to explore the history and ramifications of the Weave. Where did it come from? How many different ways can you use it? How would the rise of Renaissance-like ideas about science and technology impact it?

2. Play With the Mythos: "Mythos" refers to the game's story backbone - the big picture history of the game world, all the assumptions about how the game world came to be the way it is and where it's going. By adjusting specific "facts" within the game mythos, you can come up with an entirely different form of the game that's still recognizable.

Example: In Mage: The Awakening, the mythos states that mages can use magic because their souls are "awakened" to the true nature of reality as something supernatural and that they all inheret the legacy of the ancient fallen civilization of Atlantis. As a variant, I decided that, instead, mages could use magic because they are the descendants of humans crossed with dragons, and that it was the trace of dragon blood that "awakened" a mage. Atlantis was the place where dragons once ruled, until they were overthrown, causing Atlantis to fall. This had ramifications for who the various Orders were and what the different Paths represented. The Exarchs became the Old Wyrms - the surviving dragons seeking to reestablish dominion over the world, and the Oracles that established the various Watchtowers existed to thwart their plans.

3. Play in a Mirror Universe: A classic trope of science fiction is one that lands the heroes in a mirror universe where everything is the moral opposite of their own. All the "bad guys" are the "good guys" and vice versa. Sometimes it makes for a more interesting game to switch the "good" and "bad" sides in the game and trying to justify it with an altered game mythos.

Example: What if, in the Star Wars universe, the Sith were the good minority within a corrupt Jedi order? What if the Dark Side of the Force was aligned with freedom and self-determination through the expression of passion and aggression, pitted against another side that was more interested in a kind of galactic fascism in which were trying to turn everyone into the docile, accepting followers of a corrupt elite?

4. Play In a Different Period: Every game world mirrors some slice of human history. Some times it's fun and exciting to set a standard game in a non-standard time period. A word of caution - make sure the historical backdrop is just a backdrop. It's there for flavor. If you start to worry about historical accuracy, then the setting becomes the star of the show, not the players.

Example: Think of Pathfinder set in the Wild West, or Call of Cthulhu set in Middle Ages Europe.

5. Tweak the Rules: This is the trickiest to pull off. But sometimes you love a game but hate the game's core rules, or at least some aspect of them. If you feel experienced enough, tweak the rules with a big house rule that you make clear to your players before the campaign starts. If not, it might be best to just borrow from a set of core rules you DO like.

Example: Adjust the core die mechanic for GURPS so it works more like the d10 pool system of World of Darkness. Both are point-buy systems, but if you feel the d10 system is more elegant, why not use it instead?