There is mainly toe steps for installing Alexa Ranking,Actually Alexa ranking Is needed for better SEO Optimization .
Go to Alexa Traffic Widgets
Enter your blog address in the fields, for example -> http://mobileappsgalaxy.blogspot.com/2013/05/relax-melodies-premium-paid-apk.html
Then click the button “Build Widget”
Then there will be a page that shows the size and shape 3 different widget, choose which one you prefer.. Copy the HTML code contained within the column into notepad or word.
Step Two :
Go to Blogger–>Layout–>Add a gadget
Paste the HTML code that was saved in the notepad into the fields. Then click Save. Continue to completion. Hopefully with the installation of Alexa widget.