I'm a newcomer to Brackey's jams but I'm a veteran in general.
A few things for newcomers to jamming:
1. Don't try and go long hours and subsist on junk food and caffeine. You'll end up burning out and may even lose motivation. Have normal meals and get sufficient sleep. It'll help you in the long run!
2. Like OSmart said in the original topic, when brainstorming you can feel free to just write down whatever comes to mind, but when it's down to finally settling on an idea, be sure to choose something that you can comfortable complete in the time allotted. Nothing feels worse than having to cut exciting features because you are running out of time. Keep your ideas in scope and make sure to avoid scope-creep!
3. If possible, have friends (or if you're on a team, team members) play test your game and encourage them to give honest constructive feedback. After you work with something so much in such a short period of time, you may become blind to obvious problems. Outside perspective is always helpful!
4. Most important of all, in my opinion. Have fun. Don't stress out. Game jams are supposed to be about the experience and not necessarily about the finished product because you learn new things even from failures and there is nothing saying you can't continue with a product should you miss the submission deadline. Who knows, it may turn into something really cool you want to keep polishing!
I look forward to everyone's advice and submissions. Happy jamming!