You can create your experiment. All you need to do is give Ad-type, Ad-style and multiple changes you like to view. You can allow or deny ads.
You will have to compare the original ad settings to that of your variation. It might take few days to observe the results. Thereby, in the end you will get to know which settings were good.
You can even setup automatic experiments by going to Optimization tab, this will save your time and effort.
The stronger a light shines the darker are the shadows around it.