Important Strategy Tips: 

First, focus searching does not cost anything when in "transaction billing" mode (i.e., charge per search, print job, etc.), which is often the case. However, every time you edit a previous search you are being charged for a new search. Consequently, always, always, always use focus searching to revise your search.

Second, build your search slowly using focus to create your own limited database for searching. Trying to build a complicated search all at once, with numerous terms and connectors, often results in error messages and unexpected results. Sometimes relevant documents are missed.  Since focus searches do not incur additional charges, it is often a sound strategy to build a search slowly in steps, with the initial search using only a few terms and connectors.  This way you can see what happens when each additional term and connector is added.