Speeding my game making process

So a few days ago I joined a 9 days game jam and tried to make a 3d game with the main goal being to improve my speed and the results wasn't that great.

I made the game but it was missing polish and also audio with maybe also having a lot of bugs but I saw a little improvement in my speed so I wanted to challenge my self more and also get some useful tips.

I want to make a game in 7 days only so I need your help in choosing the theme tell me what theme that can be fun but also difficult to make and I show you the results at the end and if you have some useful tips I would love to hear them.