I secured 93% in ICSE boards 2008. My suggestions are as follows:-
1. It is very important to give almost a whole month, expecially February, solving last 10 years board papers. It is extremely helpful. Do them sincerely. Write them down, time yourself, and check honestly.
2. Nice handwriting, presentation and explanation will fetch you marks. Mugging up is good for state boards. For national boards like CBSE, ICSE, its better to write what you understand in your own proper words.
3.Have faith in yourself. Study hard.
Lastly, i repeat again, do solve previous year's papers!! All the best!