I'd say pick an old Atari 2600 2D game and remake that, something real basic that you can finish and break down into clear parts.
One I have been meaning to do for fun is remaking the home-brew Halo for 2600 https://en.wikipedia.org/wiki/Halo_2600 but with a different theme, I was thinking mad max and have the player find parts of his car while fighting thugs and so on.
I'd start with;
Adding the player
- I'd need to add controls to move the player
- I'd add animations to the player for left and right directions.
Add Screens
- Decide how I am going to have the player move from screen to screen
- How do I know what screen to load if the player move off the screen to right etc.?
- How do I design each screen, placements of objects etc.
Add objects and pickups
- Decide how I put objects, tress etc onto a screen
- Same for pickups, do they re-spawn on a timer?
Collisions
- Now we have objects so I'd look at player collisions vs objects and pickups.
Add bullets
- I'd probably go with a Type for bullets so the same code can be used for the player and enemy.
- Allow the player to shoot bullets and disappear when it hits something etc.
..... and so on until I create "a game".
