I have three main tools that I use to prep for sessions.
In addition to these physical methods, I also spend time throughout the week just thinking & planning about the next session. Lets break these down.
The page of notes is what I use session to session. Here is a redacted version of my notes from session 12 The page has seven different sections
Events is reserved for things that I think have a very high likelihood of happening. I've planned these out, I generally have encounters or ideas for how they will play out and transition between them.
Hooks, on the other hand, are mostly just ideas that I have floating around. These can vary from week to week as I plan and think. In the Session 12 pdf, two of the hooks are hidden because they haven't happened. The remaining hook is an early version of the Torlan Mroranon mission. As I planned this hook out further, the details of the story and names of characters shifted.
DND Beyond is fantastic for planning & running fights and creating NPCs. Kobold Fight Club is also a good tool for planning, but doesn't allow for running encounters or viewing the stat blocks of creatures. I'll admit that there have been times where I have thrown together an encounter minutes before running it, that's how easy DNDBeyond's encounter features are.
OneNote contains all of the continuing information that continues throughout weeks. Its a good place to store NPC information, as well as character backstory reminders.
One useful page I have just contains information about how different parties in Eberron relate to each other. This is useful for planning out larger story arcs and tying more minor story arcs to a larger picture. By creating a board like this, I am able to connect different subplots in a more meaningful way, as well as plan for potential future threats and story lines.