Begin planning your video game using something like this video game planner. If you are looking for a simple first game to start with, use this design worksheet to plan out a game with a player, an enemy and goal. Next steps will be to go through the typical video game development process of:
Design: creating a storyboard for your game & identifying/creating images & sound
Develop: working your chosen game design platform, you will begin programming your game
Test:
functional - testing the game and fixing any bugs you find;
usability - having peers, friends and family try out your game and getting feedback about ease of use and playability
Evaluate: self-evaluating your game
Create a storyboard for at least 1 level of your game. Here's a sample storyboard for inspiration.
Now that you've gotten familiar with the game design platforms, consider what the pros and cons of using each platform might be for you as a game designer and then choose one to use.
It is important to set expectations for your game, especially if you are working in a group and/or you are under time constraints. This will help you prioritize your work. Here are a couple examples of classrooms brainstorming expectations for all the games created in that class.