"But if I don't get all the way there by the time the semester starts, if I've really thought through the learning outcomes, and I’ve really thought [through] their assessment [...], I'm going to have the big milestones done and then I'll be able to just keep up a couple weeks ahead, maybe a day ahead." -- Bonni Stachowiak, Inside HigherEd 05/13/2020
First, start by aligning your WHYs with what you want the students to understand, or your overarching big picture learning goals. These are your Enduring Understandings and Essential Questions.
Write down your educational purpose and your course goals. This is available as a worksheet in the How workbook.