Comparing the conversion rate of your app with the average rate by category allows estimating the results of the ASO campaign.
Each category has its own average conversion rate that differs month to month. To find out average conversion rate for your app, use the AppFollow Benchmark.
E.g. you have an educational app and it has the conversion rate App Units / Impressions of 2.6% in the United States. The average CR by the category in the United States is 4.8%. So, you may consider what else you can do with your app page (Title, Icon, Screenshots and Avg. Rating) to increase the conversion rate.