Top 7 Important Game Design Principles

Set Clear Goals and Objectives. Goals and objectives provide a pathway for the players to follow in the game. ...
Engaging Core Mechanics. ...
Maintain Game Flow and Player Experience. ...
Balancing the Game. ...
Offer Feedback and Rewards. ...
Playtesting. ...
Sound Design.

Here are the five most critical components of outstanding Learning Games:

Goals and objectives:
Rules and/or Instructions:
Interaction:
Conflict (and/or competition, challenge, opposition)
Outcomes and Feedback.