RPGs are large complicated systems designed to manage the physical, or narrative, based rules that the world a game takes place in works. They are often filled with little nuances and tricks to help scale difficulty or to manage how things work. Because of this it canbe very easy to forget a rule, or misinterpret how one works based on how other rulings were made around that rule or how the game has played. Because of this, I often find it helpful to - every now and then - go back to the rule book and reread a section or two. The trick then is to choose which sections you are going through. So how do you do that? Well, that's part of what I want to discuss here today.
When reviewing rules I like to sort them into relevant and irrelevant sections. A relevant section is any section that is likely to come up in the next session or to feature prominently in the coming section. Because of this "combat mechanics" are one section that is almost always relevant in games for me. This step may seem obvious, but it can be important. There is no point in me wasting time reviewing combat, or mass combat, rules if the next session is going to focus almost entirely on social combat and how players buy and modify gear, right?
Prioritize Relevant Sections
After I have the relevant sections - to be honest I mostly just worry about the coming session and maybe the one after it - it is time to prioritize them. This is just as simple. Whichever section I feel I know the least, or I haven't reviewed in the longest, has the highest priority. Why? Because that way I'll have the most time to go over them.
For example, in my Shadowrun game three players are planning to initiate together soon. I am also not very familiar with the magic rules. As such, the Magic system needs to have a higher priority than the combat section because combat I know relatively well - and review frequently because it comes up frequently - but magic is complex, scary, and until recently was a very small part of the game.
Begin The Review
This is the easiest part. Once you have the sections you want to review,and the priority for those sections, all you have to do now is read. I recommend reading slowly. Try to ingest and digest the rules as you go. Think about what they mean. Think about how they can make things work in the game. If there is a specific modifier for shotting whle running, then perhaps you should think of ways to give your players reason to shoot on the run. At the same time think of ways to use the rules to make things go quicker. Even if it is just knowing the rule to make things go faster it can help.
Finally, look for anything you've gotten wrong. Maybe you thought something had a steeper, or lower, cost than it actually did. Maybe you've been calling for the wrong skill to resolve a certain action. Maybe there actually is a dedicated rule to what happens when you put the back tire of a motorcycle on a vampire's head and gun the engine. Look for it, find it, and try to remember it.
Communicate With Your Players
Finally, let your players know what you have found. Also let them know if you are going to stick with what was the case before or what you now see to be the case. This is important because there is a good chance that you'll find you handled something wrong, but your players will pick it up as a new ruling. Then, when you explain that you are simply going by the book someone may feel bad because they got 'screwed' by the old ruling. By acknowledging that you re-read and saw things you've done wrong you do two things: you affirm that you are standing by what hapened previously (unless you are not) and that you may have not done things by the book. You also establish that from this point forward things are going to be different.
Either way, it also lets players know about the clarification and lets them ask questions. So it is an awesome thing to do and get out of the way.