Before taking on a given challenge, the player gets to make some choices that affect their odds of success. This might be healing up before a battle, handicapping the opponent, or practicing in advance. You might set up a strategic landscape, such as building a particular hand of cards in a card game. Prior moves in a game are automatically part of the preparation stage because all games consist of multiple challenges in sequence.
A sense of space
The space might be the landscape of a war game, a chess board, the network of relationships between the players during the bridge game.
A solid core mechanic
This is a puzzle to solve, an intrinsically interesting rule set into which content can be poured. An example might be “moving a piece in chess.” The core mechanic is usually a fairly small rule; the intricacies of games come from either having a lot of mechanics or having a few, very elegantly chosen ones.
A range of challenges
This is basically content. It does not change the rules, it operates within the rules and brings slightly different parameters to the table. Each enemy you might encounter in a game is one of these
A range of abilities required to solve the encounter
If all you have is a hammer and you can only do one thing with it, then the game is going to be dull. This is a test that tic-tac-toe fails but that checkers meet; in a game of checkers, you start learning the importance of forcing the other player into a disadvantageous jump. Most games unfold abilities over time until at a high level you have many possible stratagems to choose from.
Skill required in using the abilities
Bad choices lead to failure in the encounter. This skill can be of any sort, really: resource management during the encounter, failures in timing, failures in physical dexterity, and failures to monitor all the variables that are in motion.