When you collect your data, you need to record your results as you do it. In order to do this, you will need to design a recording sheet.
The recording sheet needs to give you room to write in your results. It should allow you to fill in data at each of your sample sites. There are several examples of recording sheets on Moodle - you could modify one of these, or make your own from scratch.
The links below will take you to recording sheets for different topics. These comprise all of the variables that you could collect for each topic. You do not need to collect too much data - 3 or 4 variables (bits of data) will be sufficient.
A good recording sheet will make it easier to keep your data organised and will enable you to transfer your data to Excel and help you to draw graphs at a later stage. It will reduce confusion ("where did I collect the data on this scrap of paper? Was it before or after the data on that scrap of paper? What does the number 2.46 mean on the back of my hand?") and therefore make your results more reliable.
Make yourself a recording sheet.
Topics - Example Recording Sheets