Create a new Scratch project
Delete the default sprite if needed
Add a player sprite
Add a ground sprite or draw platforms in the backdrop
Set up variables for x velocity, y velocity, and gravity
Use arrow keys or A/D keys for movement
Make the player move left and right
Apply gravity to the player
Make the player jump when on the ground
Use collision detection with platforms
Stop downward movement when touching the ground
Stop upward movement when hitting a ceiling
Stop horizontal movement when hitting walls
Add a scrolling camera if the level is larger than the screen
Add collectible items
Add enemies or hazards
Add a goal or finish line
Add a restart system when the player falls or loses
Test and adjust movement speed, jump height, and gravity
Add sound effects and costumes if desired