The purpose is to provide enough detail that a competent worker could repeat the experiment. Many of your readers will skip this section because they already know from the Introduction the general methods you used. However careful writing of this section because for your results to be of scientific merit they must be reproducible. Otherwise your paper does not represent good science.
• Exact technical specifications and quantities and source or method of preparation
• Describe equipment used and provide illustrations where relevant.
• Chronological presentation (but related methods described together)
• Questions about "how" and "how much" are answered for the reader and not left for them to puzzle over
• Discuss statistical methods only if unusual or advanced
• When a large number of components are used prepare tables for the benefit of the reader
• Do not state the action without stating the agent of the action