SCRUM
SCRUM is an agile project management method. It features many elements, but for planning in the sense of success, we consider backlog, sprint, and a daily task list. There are electronic tools to support SCRUM, but most often it is enough with several post-its or an excel sheet.
Backlog
The backlog keeps all the tasks that are important for your goals. Often, it is an advantage to collect them per goal, in particular, when there are many tasks. The tasks can be big or small. Generally, they should fit easily into one day, so somewhere between 30 minutes and 2 hours is perfect. You might also want to keep some sub-goals that amount to more significant tasks. These sub-goals should be marked appropriately, and the task related to them is to make the more detailed planning for this sub-goal, i.e. create smaller tasks out of them.
Tasks in the backlog are not active so that you can have plenty of them. The main idea with the backlog is to move the tasks from your head onto the backlog. This way, you do not have to think about them before starting to work on them.
Sprint
Tasks become active when you move them from the backlog to the sprint. A sprint is just a period for you to work on your goals. It is often an advantage if the result of the sprint is something visible, but just ticking off some tasks also works fine. The sprint period should be time-bound and not too long, so something like 1 or 2 weeks or a month work well.
From the backlog, you move tasks into the sprint based on importance and urgency. Make sure that the tasks moved to the sprint can be finished within the sprint. You always aim for success, and here that would mean you have achieved your sprint goal, i.e. finished all the sprint tasks. If you cannot finish the sprint tasks in the sprint, you move them back to the backlog.
Daily List
From the sprint, you move tasks to the daily list, again based on importance and urgency. Also here, you want to have success, which means that you finish the daily tasks on the day. If you cannot finish the daily tasks on the day, you move them back to the sprint.
Sometimes you finish just part of a task, and then the day is over. In this case, you mark the task as done and add a new task for the remainder of it. Sometimes a task is done from your part, but not finished, for example, when you wait for a confirmation. It is a good idea to keep such tasks in a waiting list and mark them as done when they are complete.