The important thing in subject finding is to get a starting tip to focus your thoughts. Any dictionary will provide you countless starting points; sometimes a single word will suggest many subjects. Jot down all the ideas that occur to you and select those on which you can say something of interest to the average reader. Sometimes one word will frequently suggest another. Of course, there are other ways in finding ideas like Dickens – he drew his material from the London streets. Richard Jefferies from the hedgerows and fields while Conrad from the sea.
Furthermore, looking for ideas is amusing than waiting for them to come your way. Wherever you live there are people who are ready to give you interesting facts drawn from their special experience – provided that you make the right approach for them. Keep your ears open. There are lots of specialists around you – specialists in food, sports, education, housing, decoration and etc. All these people have expert knowledge and they may have interesting things to reveal to you about current trends in their particular field.
For more details: The Dictionary of Subjects and Ideas