Depending on how serious you want to take it. There is a website for stardew predictions, stardew checkup to help you know what's missing, and a tool for planting to know when to harvest.

Lots of tools to plan.

I also keep a notepad open but I make notes. Important birthdays, which rarecrows I have, crop numbers and things needed, fish in looking for in particular seasons and weather.

I set my goals and work towards them.