First, you should write down an hypothesis
There's also a different scientific experiment which is about it having a dependent and independent variable
You should record when you change the independent variable, cause there's a possibility that the dependent variable could have been affected against it
Though, I recommend to only change one variable in an experiment, cause combining them and making multiple combinations to see who effects who can only lead to confusion and makes the experiment more difficult
- I hope this helps, have a nice day