Well... what u guys study in sec sch now will have abit of
relevance in JC. For example, u guys will learn more in depth about
Cold War and something new called Global Economy or Religious
Fundamentalism in JC. some schs will spot the syllabus for u. As
for SEA history, u will learn all abot ASEAN, Challanges to
Independence for SEA states, Decolonisation Process for SEA states
and Interstates Tension. Same for SEA, some schs will spot the
syllabus for u. it is content heavy and be prepared. 
*edit* oh yes. for H2 history. if u wan to score A. u must have at
least 10 dates in ur essay, a few historian quotes, evidence of
further reading and nice topic and echo sentences + conclusion.
CONCLUSION is the most IMPORTANT sentence to score A. more than 4
pages, more than 5 body paragraphs. 