To manage the gamejam time, I set myself some rules:
1) Make something using previous knowledge. I knew I wouldn't have enough time to finish if I went and tried to make the game learning while the jam was going. I wrote about what previous knowledge I reused in this jam in my project's page.
2) Only try one or two new things, to acquire new knowledge during the jam. In my case it was to try out Unity's Shader Graph and the LeanTween library.
3) Keep the scope small and simple. In my case the base scope was: infinite map handling, item pool handling, player movement (left, right, jump) and health and score handling. If there's time, expand a little.
4) Make sure the game includes volume control settings!
5) Keep the UI simple but consistent. I made sure to use the same font on all the game. If there's time left, polish with animations and transitions.
6) Start by building the basic systems and core game loop. If there's time add bells and whistles later.
7) Don't spend too much time searching for assets. In my case, I needed synthwave music and searched on a couple of public domain music sites. There were probably a hundred different songs to go through, but I settled for one I found in the first 30 minutes.
8) Test the build (WebGL) on the itch website at least two days before the deadline to fix any last minute bugs or compatibility issues.
9) Save one day for uploading the final build and preparing the project page with screenshots, animated gifs, a background and a banner if possible.