Making a game for a jam is in some ways fundamentally different from making a game in general, and in some ways much the same. Everyone works in a different way, but here are a few tips I think are helpful when making games for a game jam, especially if you haven't participated in many jams before.

1. Keep it short and simple. More short and more simple than you probably think. It is a way better position to be in to have finished your game early and have time to polish it up and make it great than to be scrambling to get something completed as the deadline fast approaches. Plan a game you think you can finish very far ahead of the deadline (and you'll probably still be scrambling at the last minute).
2. Don't do tasks in order. Do not design your game, then write your dialog, then draw your art, then start building your game, etc. Do all of it at once as needed. Use the iterative method, not the waterfall method, if you are familiar with those terms. Start building the game immediately with only the most basic game design. Flesh it out and make the things you need when you get to the point when you need it. This gives you the chance to revise on the fly and scale up or down your game based on the available time.
3. Get something playable from beginning to end as soon as possible then polish. Resist the urge to polish anything before you have a completely playable game. (hint: A lot of your art falls into the polish category. So does all sound and music) Turning in something that lacks in polish is way better than turning in a game that is missing essential features or story, or not turning in anything at all.
4. Don't get bogged down in anything. If something is taking longer than you thought or you're having trouble with it, skip it for now and work on another part of the game. You can come back to it later when you have time and have mulled it over in your mind more. Or not. You may decide that feature isn't worth it and do a quick redesign to get rid of it.
5. Sound and Music helps a lot. Don't forget about it! But also don't do anything with audio until you have a completely playable game (see #3)
6. Remember to make time to build your game and test your build. This can take longer than you think if it doesn't go the way you planned right away! Ideally you should plan to stop implementing anything new a whole day or more before the deadline so you can fully test your build. Be sure you're testing your builds, not just the one that runs in the editor or engine you are using.

These are really just my opinion but I hope they're helpful. If anyone has any other tips or something to say about mine, comment below!