1. Keep things simple one main mechanic is a good idea as less complex games are easier to pick up and play and it will leave more time for you to polish out the game.

2. Few minutes of gameplay is more then enough we have a lot of games to review and we just need to see what the game is about. 

3. Don't upload at the last moment not only can you drop a link for people to play test it and fix anything before the jam start and upload new fixed build you also will have time to work on the cover image and screenshots if they look good you'll have a higher chance of beaing rated and having less then 20 ratings lowers your score.

Mentel already made great tips, but id like to give you some too! (I also am somebody who's relatively new to game dev too!)

1 - If you are stuck on an error you cant resolve even after quite a while of trying to solve the issue, you could try to ask ChatGPT what is causing the error, just copy the relevant lines of code and type something like this "Im getting a "(error message here)" error in (game engine (and engine version if needed) here), can you find the cause for me?: (paste code here)"

2 - This is very obvious, and you've probably heard this before but please take a break every once in a while, like for every hour, take 10 minutes to relax. This will help a lot.

3 - Create concept art, a rough draft of a story if there is one, and more beforehand. This will help you have a clearer path during development, and should always be done (in my opinion)

Creating concepts helped me figure out how i wanted the character in my game to look, how i wanted the scenery and music to look, and more. so i have no doubt that this could help you too!

the most important tips are just keep the game simple and take breaks, eat and drink.

Make sure to properly plan for an idea that you know will work. It is a waste of time to jump in with a half complete idea and realize it won’t work out in the end, resulting in you needing to change ideas.

The most important thing of all... Try your best. 

... And what makerk said

1) Come up with concepts for games for each of the theme before the jam starts.

2) Plan what you can finish for each day and try to leave one day blank for everything you haven't finished/fixing bugs. But don't get discouraged if you are behind because plans never work out exactly like you expect them to.

3) Try to tackle new challenges because that's what jams are about.

Keep the scope small.

Don't Start your game dev journey by creating everything from scratch, instead learn how to use made assets and how to flip them to look more original and unique

Secondly, you can use Chat GPT to help you with the coding side of the game,

Last thing, consume content and feed your mind with ideas and visual Arts