Guidelines for developing search engine

I've been asked to research the redevelopment of a university search engine. The existing search engine looks for students and how much funding they have through by way of a grant.

The existing search engine is an expert system that has about 40 fields. Users typically only need 4 or 5 fields but these can vary depending on the task.

I'm approaching this by building a basic prototype which I'll use to drive out deeper needs from users.

But my question is this: is there any specific guidelines or evidence that would help me build a good search engine? What things should I be looking to build? What features?