The method should be a clear and precise procedure of how the experiment should be carried out. It should be precise enough that the teacher should be able to conduct the experiment while only using your practical write-up. Start off with elaborating on your preparations of materials. Then talk about setting up the test tubes and placing a varied amount of substrate in each one. One the practical is all ready, instruct the reader to carry out the testing of the substrate concentration. Don't forget to record results and talk about reliability, validity, the variables, diagrams, risk assessments and to write it all in 3rd person. Have fun