Beyond the Rules
In addition to officiating the rules and employing the proper mechanics, there are many other areas that do not fit into the headings at the top of the page (Runner, Batter, Pitcher, etc.). Some of these, like managing substitutions and proper appeals, actually are rules related, but most are not.
I've included those few rules-related subjects because they tie in so closely to game management. Most of these topics, however, belong in the library of umpiring conventions that have developed over the nearly two centuries of umpiring baseball.