Newspaper keyword searches can be surprisingly tricky -- rather than using many keywords, only use two or three at a time. Use the filters to narrow your search, focusing on a specific time period or location. Use newspaper indexes (See tab) to identify key newspapers related to your topic. Use subject/theme specific newspaper databases to narrow your search still further.
Full list of newspapers
EBSCO
ProQuest
Gale
WorldCat
GoogleBook
British History Online
Some Database like Chronicling America have a special drop-down feature for proximity searches built into the search commands.