Use double quotes around phrases to search, eg. "Lochnagar Mine" will match fewer terms than Lochnagar Mine which returns all pages with Lochnagar in as well as all pages with Mine in.
Add + in front of terms/phrases that must appear in results, eg. +Lochnagar +Mine will match pages with Lochnagar AND Mine
Add - in front of terms/phrases that must not appear in results,eg. +Lochnagar -Mine will match pages with Lochnagar that DO NOT contain Mine
By default all searches with two or more words in the search term are treated as thought there was an AND between them (e.g Lochnagar 1916 1917 is treated as find pages which contain Lochnagar AND 1916 AND 1917). But you may have wanted pages which contained Lochnagar AND 1916 OR 1917. To do this just add the word OR, in capital letters, e.g. Lochnagar 1916 OR 1917 will give you results about either one of these years