I made a query then switched to SQL view to see what was actually happening. Eventually I got good enough to clean up the Access SQL to remove the redundant garbage that the query builder would put into the sql. Also, whenever I got stuck I would do a google search. I never had to buy a book, there is so much good information for free online.
one more thing... I am a Business Objects developer/administrator. If you're a user, and your BO admins are building thier universes properly you would not have any need to be using SQL. It should all be drag and drop. That's one of the reasons for giving users BO is so they don't have to learn SQL.