The first rule of writing a game is to begin at the end.

You must be absolutely clear in  your own mind what 'winning' looks like.

It doesn't matter what genre, style or medium you're working in, in order for your players to understand how to win, you must have crystal clear clarity about they win.

And this is trickier than you think.

For example, I'm mentoring a fabulous young writer through the process of writing his first game, a game that will be simultaneously be published as an online game and a paperback gamebook. Hugh decided his adventure would be set in a world of medieval futurism - okay, so far so good.

When I asked him what 'winning' looked like, he replied, 'Saving the kingdom.'

Which is a perfectly reasonable reply. However my next question was not so easy to answer. That question was, 'How do you save the kingdom?'

I wanted specifics. I wanted to know if I save the kingdom, what is my reward.  And how I do I save the kingdom? And from what? A big bad? What does this big bad look like? What are their powers? What powers do I have or can I collect? Each question begat further questions, each one offering a glimpse of what the game might look like when it's completed.

All this will contribute to Hugh's world building, but there's no point building a world until you have identified exactly and to the nth degree what the player has to achieve in that world. You can - and people do - spend hours, days and months creating the most detailed world for your players to explore. But all your efforts mean less than nothing if you don't have the mist definite idea of what the player has to achieve when they find themselves there.

So before I had Hugh write a word of the game, I asked him to write an outline of what winning looks like, and that's what he's doing right now. Until he provides me with a detailed yet easy to understand synopsis of what 'winning' looks like, that is, what the end of the game looks like, there's no point him beginning to write the game.

Beginning at the end is exactly how I wrote Game of Runes, and the player knows from the beginning what they have to achieve.  Remember, the players of our games are our friends who've we've invited into our worlds, our homes. We want to be good hosts and entertain them, not fry their brain with confusion.

You can play Game of Runes below, and see how successful I was.
Game of Runes