doc on searching, and sorting

Hi,
I'm looking for a good treatment of searching through tables in PostgreSQL. I've read the doc, so I can build searches using LIKE/SIMILAR TO/~ , but it would be really useful if I could read up on strategies for executing queries (both for good results, and for efficiency).

In the absence of that, I'm currently trying to figure out if it is feasible to sort my matches as follows: I have column A and column B, I execute a search for certain words in A OR certain words in B, I'd like to sort it so that documents that match both A and B appear first, then A, then B. Or how about sorting such that the rows that matched the most words in the search string appear first? I dont know if such sorting would require joins and subqueries such that it would take up a lot of resources. Any tips would be appreciated!

Thanks.
- Luis