Microscope Plant Cell length experiment

Answer any one of the questions
So in a book there is this experiment about nail varnish to count number of cells across a diameter. There is some question I don't know the answer too such as :-
1)How to make the experiment fair.
2)Also it asks how much fields of view should you look at.
3)Finally, in june 2013 It asks to plot standard deviation on graph which is a bar chart does this mean I just plot it right next to it. (http://filestore.aqa.org.uk/subjects/AQA-BIO3T-Q13-W-TASK-JUN13.PDF)