Guidelines to develop the search engine.

I have been asked to investigate the redevelopment of a university search engine. The existing search engine looks for students and the amount of funds they have through a grant.

The existing search engine is an expert system that has around 40 fields. Users usually only need 4 or 5 fields, but these may vary depending on the task.

I am getting closer to this by building a basic prototype that I will use to eliminate the deepest needs of the users.

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