Hi, I’m in the exact same situation as you, wanting to revise for my GCSEs in 2020, get fitter, do more extracurricular activities and increase my chance of doing medicine.
I think the best way is over the next couple of days, plan every day in the summer holiday. Include outings and holidays and seeing your friends, but also revision sessions covering content from year 10. An example could be:
7am-8am, wake up and get ready
8am-9am, Go for a walk outside or do some exercise
9am-9.30am, Eat breakfast
10am-11am, Revise Biology B4-Bioenergetics
11am-12pm, Break
12pm-12.30pm, Lunch
12.30pm-2pm, Go our to the cinema with friends
2pm-3pm, look for work experience and apply aswell as extracurricular activities
3pm-4pm, English, Conflict Poetry
4pm-5pm, Break
6pm-7pm, Quizlet to revise French
8pm-8.30pm, Read book (Maybe one studying at GCSE) and plan for next day
8.30-10pm, Wind down with Netflix and go to sleep.
Planning the day ahead increases productivity for the day ahead and by accomplishing these daily tasks, helps to motivate you to continue with them.