The analysis of the competition is certainly a long and complex procedure, but just to start with, just take a look at some fundamental factors of your competitors. It can certainly be useful to repeat the same analysis made for your site so far (on indexing, completeness, speed, mobile compatibility) for each competitor as shown in the Customer Insights Course.
Wait until the bar reaches 100%, so that the analysis is complete, then go to Competitor analysis. Here you have an immediate glimpse of the situation. It summarizes everything with scores and colors to present an easily readable ranking.
An interesting picture is on social media: the number of shares on each channel is compared. So you can understand in an instant what social media your competitors are using the most (and if they are using them). Grader is a free online tool that analyzes some essential features, assigns a score accordingly, and suggests how to improve the site on these aspects.