I've joined a few game jams before and I would say keeping the scope low and learning what tasks to pioritize are very importaint. Usally I like to think of game ideas that are simple but can be expanded upon if there is still time. Or if i come up with a bigger idea i need to try to figure out which parts are the most importaint and pioritize thoes. If you are a solo dev I would just focus on programing the core mechanics untill the game is playable then slowly polish the game by adding art and sound. I also like to give my self a fake deadline or milestone goals to see if im on track to finishing on time.