Summarize:

Forget about the classic 'listen to your teacher, do your work, work consistently' strategy. Instead, think long term. Relax, enjoy and have fun throughout the year. There is really no need to work your butt off for the internal examinations or try to impress your teachers because, in the IGCSEs, "only the boards matter!". When you do homework, you can test what you know on each subject, and you can look back at it for revision. Every weekend, just read through the text. One chapter of each subject; whichever one you prefer, but, try not to repeat the same ones every time. A steady, ongoing state of learning will have you more than ready by exam time, rather than trying to cram at the last minute. Those breaks during the year provide a more relaxing, yet still work-focused, time to keep preparing consistently. If you use these times to keep learning, you won't stress anywhere near as much as those leaving it all until the last minute. This deeper learning and revision must begin well before the boards, so plan out a timetable and give up on about 90% of the fun you have been having at this point. It's serious study time! It may seem a long-term but it short in the bigger scheme of things and yet has such long-term impact, so dedicate yourself to the long-term outcome for the best.
Throw out previous thinking. Do your homework consistently during the year. Keep it in your mind that you need to get grades from A-star to C, because a D or lower is a fail. Read voraciously. Use your holidays and vacation as a time to study. Prepare in earnest from about six months, then really knuckle down at three months to go.