Definition of the problem - what is required, how many determinations, how sensitive, how accurate, what equipment is available, how much sample is available, how quick is the answer needed, cost factors, sample make up. Select a method of analysis based on the problem at hand. Obtain a representative sample.
Various samples require various techniques.
Sometimes easy others a challenge. The floor sweepings wash water. Dissolve the sample- water, acid, heat, flux Perform needed separations, oxidation to eliminate interferences, masking agents. Make the measurement. Present the Data and calculate the results.