What are the key responsibilities of a CSO Board of Directors?

I’ve just joined the board of a small NGO here in T&T and I want to make sure I understand what I’ve actually signed up for. The organisation has been around for years but I get the feeling the board hasn’t been very active — meetings are irregular, most decisions seem to get made by the ED. I want to help push for things to be done more properly but I’m not entirely sure what ‘properly’ looks like. What are the things a board is actually supposed to be doing on a regular basis? What am I legally and practically responsible for as a board member?