Take school seriously.  Your whole future may be affected by how well you do.

Treat teachers with respect.  They are giving their time and effort to help make your future better.

Make time for homework and do it as well as you can.  You need a quiet place at home where you can work undisturbed.  Ask your parents to help you if you get stuck.

Do your best in all years of secondary school.  In the UK, the work you invest in years 7-9 will determine the maximum grades you will be allowed to try for at GCSE, so they are just as important as the GCSE years themselves.

In subjects where you are in ability sets, always aim to be best in your class in each subject so that you get moved up a set as soon as possible.

Improve your English ability by reading books that interest you in your spare time.  The more you read good English, the better you will be able to use good English in your writing and speaking.

Use the BBC schools web site whenever you can in your spare time to check your progress in all the core subjects and improve your scores.

When you start to study for public exams (like GCSEs in the UK), ask your teacher for a copy of the syllabus for each subject you are studying, or get the syllabus code from school and download the syllabus from the internet.  The syllabus tells you exactly what you need to know for your particular exams, and provides a good way to check off things you know and things you still need to learn.

When you get near to the exams, ask your teachers for past exam papers that you can do at home under exam conditions.  Your teacher will usually be happy to mark this for you.  Getting practice at completing exam questions within a time limit will prepare you properly for the final exam and give you your best chance of success.