Using key words with and is the most efficient way to search. You can cut down on the number of searches you do by combining key words and their synonyms with 'or'. For instance (cat or feline), (surgery or operation). Notice that the 'or' phrase is in parentheses. The 'or' combination is ALWAYS in parentheses which insures that those words are combined first. Put the 'and' between the 'or' phrases, (cat or feline) and (surgery or operation).
If you are using a commonly accepted word combination such as "gun control" or "same sex marriage" put the words in quotes. This tells the computer that these words must be next to each other.
Another way to quickly focus your search is to use the available limits. Applying such limits as a time range or limiting to peer reviewed material can quickly eliminate unwanted materials so they aren't included in the items you have to review.
If abstracts are available, use them to quickly review your articles so you don't have to read entire articles to decide if you want to keep them.
Use the available subject headings to expand your synonym lists. There may be terms you did not consider.