Rules are toys, and the process of rules-mediated play consists of smashing their faces together like little girls making their Barbies make out. Unless a rules module is explicitly intended to be enacted solo, it should present a generous surface area for other rules to bite into. The most elegantly self-contained piece of rules design is, collaboratively speaking, also the most useless.
The principal function of “player characters” as discrete collections of mechanical traits is to furnish each player with an assemblage of shiny things to show off to other players. Mechanical abstraction is well and good, but if you abstract away the act of curating one’s collection of shinies, player engagement will suffer.
The GM, if present, is a fellow player. Ensure that they have their own toys and shinies to play with. The failure of a game to provide these is often a major contributor to why nobody wants to run it!
The most effective way of encouraging players to do what you want is to make a number go up. This applies to both to rewards and to misfortunes; a number counting up to disaster a much more visceral motivator than a number counting down to zero.
Crunch is good. The defining feature of tabletop roleplaying is that rules produce stories. The act of interpreting the outputs of the rules and the act of telling the game’s story are the same activity. Be mindful of what kinds of stories your rules want to tell; you may find that their opinion on the matter differs from your own!
Actually assembling your game’s rules is as much a process of discovery as it is of invention. In the course of designing and playtesting, you may find that your own game has rules that you didn’t know about. Where did they come from? It is a mystery.
Randomised outcomes should be made mandatory with care and restraint; randomised outcomes should be made available with delirious abandon. As far as is practicable, players should always have the option of asking the dice what unhinged bullshit should happen next. Corollary: lookup tables are your friend.
Players don’t need your permission to depart from the rules as written; granting it is arrogant. By the same token, however, it should never be unclear to players whether they’re departing from the rules as written. Let the thought process behind what you’re writing hang out for all the world to see; folks will be rummaging in the game’s guts anyway, so give them easy access.
If your game has a default setting, explain it as little as possible, but always let the rules and presentation reflect it. Seeing an entry for “poorly made dwarf” in a table of player character backgrounds will fire a group’s imagination more strongly in three words than a chapter stuffed with worldbuilding lore could in ten thousand.
You don’t need to be good at naming things as long as you’re good at puns. Wordplay, alliteration and rhyme may also serve in this capacity, as, in a pinch, may a well placed dick joke.
40,000 years ago, early humans painted hands on the wall of a cave. This morning, my baby cousin began finger painting. All of recorded history happened between these two paintings of human hands. The Nazca Lines and the Mona Lisa. The first TransAtlantic flight and the first voyage to the Moon. Humanity invented the wheel, the telescope, and the nuclear bomb. We eradicated wild poliovirus types 2 and 3. We discovered radio waves, dinosaurs, and the laws of thermodynamics. Freedom Riders crossed the South. Hippies burned their draft cards. Countless genocides, scientific advancements, migrations, and rebellions. More than a hundred billion humans lived and died between these two paintings—one on a sheet of paper, and one on the inside of a cave. At the dawn of time, ancient humans stretched out their hands. And this morning, a child reached back.
