My overall planning approach these days is fairly simple: a paper-and-pen bullet-journal-ish approach, which has a kind of fractal quality to it (much as my work logs do when I am doing that). I plan out my year, month, week, and day, each one with increasing granularity and specificity compared to the higher level, and each one in terms of the goals I have set for those higher levels. This takes some time — though not as much as you might think — but I have found it very helpful. One of my major takeaways from my personal review of 2024, in fact, was that the months and weeks and days I took care to do my planning and review were consistently the months and weeks and days of the year in which I worked most effectively at my goals and aims.
One benefit this “fractal” approach offers is making it so planning what to do on any given day is generally straightforward, because it is obvious: Pick things from the list for the week. The thinking about what to do on a given day is mostly down to thinking about which items from the list for the week should happen on a given day. That still requires prioritization, but if I have done the work correctly in picking my work for the week, even prioritization is usually pretty clear — though it can definitely also shift over the course of a week as life happens.
The same dynamic is at play at each level of planning. Planning out a week takes some time, but is straightforward if I have done a good job of thinking about what I hope and can reasonably aim to accomplish in a given month; and likewise for planning months when I have given thought to the year as a whole.
In practice, of course, there is always going to be a good deal of “flex”. Today, for example, I had nicely mapped out my day, only to find a few hours in that one of my four planned appointments had to be rescheduled and then, a few hours further along, that another had had a calendar mishap. I adjusted on the fly, as one has to. I still knew the big picture of what I wanted to get done both today and this week, so that made my adjustment rather straightforward.
This exact approach may or may not work for you, but I commend the gist of it to you!