Small, manageable, discrete goals. Focus on the most crucial stuff first. "I want to make a video game" is a huge and daunting task. "I want to have a character that moves when the player presses the arrow keys" is easy. Then you move on to, say, "I want the character to shoot a bullet when the player presses a spacebar." "I want an enemy that dies when shot with a bullet." "I want the enemy to move." "I want the enemy to shoot back." "I want the player to have a health bar that depletes when they're hit by a bullet." etc. etc.