This is my 3rd Jam and here's the usual mistakes we all makes that can be fixed right away:
- The jam might be starting the 20th, but you're allowed to think about ideas ahead.
The most common mistake people makes is to think they must only turn their brain's ON on the "Start" day, but you can save yourself a lot of brain cells from burning up by simply thinking about core concepts as soon as now. You can scribble and take notes of ideas, including sketches. I must warn you to NOT start seriously thinking of a project until the theme is given unless your idea can be universally converted to any themes. From the Game Jam Starter Kit, we can guess that there will be not much of a restriction on the gameplay since it includes an example of multiple kinds of games (it includes a 1st person, obstacle course, Puzzle and Car Racing package) so you can think of basic ideas related to the kind of game you'll be making.
As long as you don't create the assets ahead of the starting line, you can work on the project for prep. If you want to make a racing game, you can already write down idea of tracks, traps, weapons, etc. for your project. If you're making a puzzle, you can write down the kind of puzzle you think you can make.
So a trick is to buy a cheap notebook and scribble in it right away.
All those notes and ideas you will have though about will be time saved from the limited 10 days of development and also added time from those who made the mistake of not prep like you did.
- You can practice making game concepts/systems ahead.
Another thing often missed is that people don't practice outside of a jam. Like anything, practice makes perfects, but also makes you faster and more efficient. It wouldn't be a waste to practice on what you find as your biggest time waster or weakness prior to the Jam. Obviously, you can't just use the stuff you made from practice in your submission, but if you made 1 racing game (even incomplete) prior to the Jam, making a 2nd one for the Jam will only be easier. If you already worked on how to make the proper physics and inputs-action-controls for a platform games, then you just have to redo it for the Jam. You can save an insane amount of time ahead by trying stuff out prior to the Jam instead of just cramming that "trying stuff out" during its limited time.
If you're going for a story-based game, it's a bit risky because the theme might destroy your idea of a story, but you can write a generic/base setup of a story to work with ahead of the jam.
- Think small and grow bigger.
This is a Game Dev Jam... not a race for finding a cure for cancer. You don't have to think about all the complexity of an advanced game concept. Start by thinking simple and small and grow the idea as it's building up. For example, if you're thinking of making a Tank vs Tank game, don't start thinking of making all the realistic explosion, ballistic physics and having the graphic fidelity of 3D scans. Instead, make simple tank models, build a working target-shoot system with some hit system. Make that work first and, then, depending on how much time you got left start thinking of adding details, or advanced ballistic physics or whatever. Even if your idea seems like the best of the world, you got 10 days to build it, test it (as much as possible), fix it and submitting it. It's especially important if you don't know what you're actually capable off as you will most likely try to chew more than you can bite.
- Prepare not only mentally, but in real life too.
You're a family person or you got work and don't know how to put the gears in place as to live with both without burning yourself out? Well, don't be scared to talk about it with your family and even coworkers! For your family, they might do things to lift some of the "family life" weight off your shoulder for those 10 days and, trust me, if you end up with a working game by the end you'll be one of their biggest heroes ever. For your coworker, while they might not be as understanding as your family or even interested, you might find even just 1 soul who might unknowingly share your passion or just agree to talk about it and that will release some pressure from your mind. They might even see (in their mind) or think of something you have not noticed. They might be more understanding if you come at work with a zombie face too (as long as you do your job).
It's not because you work alone (or in a team) that you must keep everything for yourself (or within that team).
With that said, don't share your situation with anyone that you know would take it badly or who clearly is not close to the subject at hand. For example, if a coworker is that guy or girl that hates video games because he/she thinks it's a waste of time and he/she prefer hitting the pubs, don't bring it up with them as that's just a waste of time. Your goal while talking about it is to release some mental pressure by "emptying your bag"... not filling it with others' negative thoughts on the subject (or other related subjects).