I'm no expert but defining a managable scope is probably the most important thing. If the vision you have will take too much time, it's better to ditch it and go for something simpler.
Another thing is cutting corners in your systems. In a jam you don't need complex systems in your code- if you're on a tight time frame, go for the quickest options that work. Also, if you've made other games in the past then recycling scripts can help.
Same for art, sound etc. Go for a solution that serves the purpose of your game but doesn't comsume too much time.