You'll need a sample of whatever it is that you are wanting to test for ketones. If your sample is solid, you'll need to dissolve it. Do not use a solvent that contains a ketone group (e.g. acetone), or a solvent that will react with a ketone group. Water, hexane and ethanol are good solvents for this purpose.
 The first will be tested to show the presence of C=O, and the second to show that it is a ketone., Be careful - 2,4-dinitrophenylhydrazine is an explosive! It will go off if handled dry. A red, orange or yellow precipitate indicates a carbonyl (C=O) group., Neither reagent should react with a ketone. If your solution contains any aldehydes, Tollen's reagent will produce a silver or grey precipitate (or a silver mirror on the side of the container), and Fehling's solution will produce a brick-red precipitate.,
1st test positive and 2nd test negative = ketones.
1st test positive and 2nd test positive = aldehydes, possible mixture of aldehydes and ketones.
If the 1st test is negative but you do the second test anyway, and get a positive result, then there are no ketones, but there is a reducing agent present. Try the first test again to make sure it wasn't a false negative.
Take a sample.
Divide your sample into two parts.
Test the first sample with Brady's reagent (2,4-dinitrophenylhydrazine dissolved in methanol and sulphuric acid).
If the first test is positive, add Tollen's reagent or Fehling's reagent to the second sample.
Interpret your results:

1st test negative = no ketones.
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