As an experimental physicist this is a question I am asked fairly often (mostly by non-scientists but occasionally by my bosses). I have been trying to find a concise way of answering the question, and have so far failed. Thus I now reply with the statistically correct answer which is that most of my time is spent watching a number on a computer screen either go up or go down. The size of the number and the speed of its changing varies according to the experiment but for the most part that is what scientists do (any other scientists who disagree please state your point below).
I am aware that this is incredibly un-enlightening but I am happy to have given a truthful answer that is audience invariant. Any improvements would be welcome.