Yesterday - as of the time of this writing - was an interesting day. It was also the fourth session of my Marvel Heroic RPG game, and yes the two statements are linked. In the current event I am running for my Marvel game I am borrowing heavily from the two Ultimate Avengers animated movies. The heroes are investigating Chitari activity in equatorial africa and have thus run across the African nation of Wakanda. However, what was interesting to me as a GM yesterday were the reactions some players had to how I was GMing. The group is new to the game and still getting used to the rules, but with the action clicking along at a fast pace I essentially called an audible and just started making rulings on the fly to compensate. I thought it worked out well, but it still is worth talking about the how, why, and whats of it.
Nothing Disrupts A Game Faster...
In my experience absolutely nothing disrupts a game faster than a mechanics debate. When you have a group who truly knows a system you can run through things like combat pretty fast and by the book. After all, everyone knows the system and they know how it works. With a new system though combat is often clunky because everyone, the GM included, is trying to make sense of the system.
Because of this, especially near the beginning of a story when you are trying to hook your players into the plot, it can often be important for you as the GM to simply throw the rulebook aside and GM by the seat of your pants. Yeah, it can be scary at first, but with practice it can become second nature and is a very good skill to have in your repertoire.
Don't Be Afraid
The trick to remember whenever you toss the rule book aside, even if only for a bit, is to not be afraid. Tell your players that you're going to be going a bit faster and looser with the rules than normal if you have to, but above all just stick to your guns. Your players should catch on quickly and begin to explain to you their intent and hopeful outcomes so you can roll with things. This may come in the flavor of questions "Can I use mental domination to make them think that everyone else is an enemy?" or it may come in the flavor of more bold statements "I'd like to use mental domination to confuse them, hopefully it'll get them shooting each other instead of us." Either way though, you now have the intent and goal for the action. So, just run with it.
Mitigate Success and Failure
One of the common reasons I've had people tell me they don't like going fast and loose is because it can give the creative players a lot more power and leave others feeling left out. Because of this, you want to avoid having an action run rampant with over powered success. You should have some idea of just what a character can and can't do from how the system normally works, so try to stay within those constrains.
What this means is that if a player goes for the above example (dominate soldiers into shooting each other) you can have it succeed, but don't have it succeed so much that it ends the conflict before anyone else gets to do something cool. On the inverse, if the action fails try to mitigate the failure as well. You are taking away the chances for extreme success that the rules may normally allow for, it is only fair that you also don't punish as harshly for failure as the system may encourage.
A Chance To Shine
The other thing you want to be careful with when setting the rules aside is that you want to try to give everyone a chance to shine. It does no good if the rules get set aside for Tom and Jane but Susan and Harry have to do things the normal way. Nor does it work if Tom and Jane get to be super awesome, while Susan and Harry try for it but don't get the same kind of effect. Obviously this isn't always going to be the case. Even going fast and loose with the rules, some people are going to fail rolls or not jump at all opportunities, but you want the possibility to be there.
Run With It
Finally, don't be afraid to run with it. Some of your players will likely try crazy, but awesome, stuff during these times. If you embrace that, show you're willing to work with it, then your players will be more likely to try that stuff again in the future as well. This is one of the ways to get the game really going and to get strong mental images in everyone's head. It is also a great way to really up the property damage as the players are suddenly fine with trying stuff like jumping the bus onto the dragon or crashing the boat into the harbor to try and get an effect they want.
Sometimes it is best for the game to just set the rules to the side. Especially if you, the GM, has a concept for how they work and how you want them to work, but your players aren't fully sure how to do everything they want. In my opinion, I'd hate to lose out on an awesome session because I was too focused on how the book said I should do something. Maybe your group is different, but even if it is just a once in a while thing you can have a lot of fun with this.