Typing in any of these operators will get you a more refined search.
- To find messages matching keyword A or keyword B, type "OR" in all caps, for example: from:amy OR from:david.
- Find specific types of files with "filename:" for example: filename:jpg.
- Search messages within a certain period with "after:" and "before:" for example: after:2014/04/30 before:2014/05/06.
But wait, there's more! For All of the possible search operators supported by Gmail, click HERE.