Dress codes vary slightly according to size of company and industry sector. It is probably safest to err on the side of caution and wear standard, smart business attire. Men can wear dark suits, shirts and ties and women will not feel out of place in conservative business suits (although trousers tend only to be worn on informal occasions.)
Bear in mind that it can be very hot and humid at certain types of the year and extremely cold in the winter. Ensure that you have the relevant weight and type of clothing to meet the climatic conditions you will encounter.
Umbrellas and raincoats are useful throughout the year as rainfall levels are high.