I might not be an experienced vet but I do remember what i regret doing in my 1st couple game jams:
- setting expectations too high
- not figuring out a temporary core gameloop or ending (waves/cutscene, something that makes the game not boring too, endless mode can be a post story thing)
- procrastinating (please make some sort of list & check it off. You have a whole month but I'm sure you also have a life)
- focusing on small details (those'll matter later when your game needs some extra spice but make a prototype 1st & see where you wanna take the idea)
- trying to make everything yourself (if its not broke & it looks aight feel free to use it, theres no rules stopping you. Find a balance between your own stuff though so it doesn't just look like an "asset flip"
- using too many tutorials (if your really stuck on something it makes sense, but if your entire game is built off the back of Brackeys your not going to know how to fix anything & will find yourself in "tutorial hell." Only you can (somewhat) understand your spaghetti code lmao c: