Possible Clues:

• Modifying words
• Notices about 'Shine', say, or 'Truly, Madly, Deeply', for example
• Now and then
• Parts of speech
• Perhaps 'hurry, compare and buy' and 'fairly and squarely' for example
• Hither and yon
• Slowly and surely
• They qualify or modify other words
• Quickly and quietly, for instance
• Purely and simply, e.g.