I am so glad because the Jam for All BASIC Dialects(#1) will start after 5 days! I look forward to every entry! I expect that many entries will be so creative!

My advice:
It is a game jam. Thus it is only for fun and practice. Therefore, don't be too nervous.
I encourage you to keep it simple in order to prevent scope creep.
Nevertheless, you can also make it however complex you are comfortable with.
Gameplay and graphic are the two important aspects in a game. Designing an appropriate and interesting gameplay for your chosen theme is the first step. Looking for suitable graphics or Creating suitable graphics is the second step.

Okay, this is my advice.

Finally, if you can help to let other programming hobbyists know the information of the game jam, they will also be able to join this enjoyable jam!