Pick a day to write everything in your planner.Pick a day, ideally at the beginning of the week, where you set aside a good fifteen or twenty minutes to block in everything you know is going to happen in the week ahead. If you work, make a note of your regular work hours; if you're in school, write in your class schedule.
As you're plotting, you can alternate between pen and pencil: pen for more permanent events you know are unlikely to change; pencil for goals or appointments that have more flexibility.
After you've finished writing in everything you know is on the agenda, bring your planner with you to your appointments and keep it updated throughout the week. Updating will take less time once you've mapped out the big picture.