Do assume that your reader has played a game before.
Quotes about writing game rules
If we want to make some progress in the recognition of the cultural nature of games, everyone has to get involved, especially publishers, by having their rules written and corrected, if not by professionals, at least by people who have a minimum command of the language. There’s no shortage of such people in the hobby.
The rules text is not your game, it is your game’s user interface. It is the button pad on your cell phone; the remote control to your cable or satellite box; the steering wheel, gearshift and pedals in your car. It is the way players (in the absence of a teacher) connect with your game and it needs to be designed as rigorously as the rules and procedures. Players cannot fall back on mashing your game’s buttons, poking through its menus or clicking hyperlinks at random.