Start revising as from Lower 6. Master all Lower 6 chapters in the summer holidays (Nov-Dec) before your Upper 6.
Make sure to complete as many past papers as possible.
Make your own revision notes in a separate notebook.
Know your weaknesses and common mistakes - make a note and go through them regularly.
Have a work-life balance: Physical activities, go out with your relatives to get a time out of your studies, hobbies.
For the practical paper, regularly prepare dishes at home (e.g. every Sunday). Try to find some innovative ways to decorate/garnish your dishes. Focus on local ingredients.
Make your own notes from reference books. This will help you master the more challenging chapters. Also, complete as many MCQs.
Have a vocabulary notebook. Try to complete one essay per week. Keep abreast with the world's events (use BBC, The Guardian ...)
Read magazines to get facts for your essay themes.