The Standard Laboratory report
Laboratory write ups tend to vary from one educational establishment to the other, but a general pattern is found by comparing different laboratory reports, generally the expected format is one of:
Title, Date and name of experimenter: This needs no explanation.
Aim: This section should define the purpose of the investigation
Hypothesis: formulate a testable hypothesis and explain the hypothesis using scientific reasoning.
Apparatus: Usually a list of apparatus and a schematic showing how the apparatus fits together.
Method: identifies the relevant variables (dependent, independent, control) and explains how to manipulate them.
Results: Typically the results are given in a table and then as a graph where appropriate with error bars.
Conclusion: Put here what it is you have found. This may just be a statement of a numerical value, or a simple statement that relates your results to your hypothesis.
Evaluation: evaluate the method commenting on its reliability and/or validity, suggesting improvements to the method and making suggestions for further inquiry when relevant.
Reliability: Refers to measurement of the data. This depends upon the selection of the measuring instrument, the precision and accuracy of the measurements, errors associated with the measurement, the size of the sample, the sampling techniques used, the number of readings.
Validity: Refers to the success of the method at measuring what the investigator wishes to measure. This includes factors such as the choice of the measuring instrument and whether this measures what it is supposed to measure, the conditions of the experiment, and variable manipulation (fair testing).
You are not constrained to use this format but it is one which has become familiar to many experimentalists as it does follow a logical path. Whatever format you prefer to use, make sure it can be followed easily by somebody who is not conversant with your work!