I find that one can start to drift in ones photography unless one has a goal in mind. For that reason I always have a couple of projects on the go.
In my day job working in IT I occasional have to travel and this nearly always a trip through or to London.
I aways take a small camera with me, either the Leica M4 or M8 and have spent the time while waiting for trains looking for interesting imagery within the train stations.
Being able to continually revisit an area allows one to develop themes and thus put together a nice set of photographs.