Google Page Rank is given on the scale of 10. The most linked sites get higher page rank and get preference in Google search results.
To increase page rank, read How to Increase / Improve Google Page Rank

Alexa Rank is traffic rank for a website, collected by Alexa Toolbar which millions of users across the world use. Alexa rank is important when it comes to selling advertisements or paid reviews on your website or blog.

To improve your alexa rank, check out 10 steps / ways to increase your Alexa rank by 100% in 1 week OR Use Vinnoite Ping Tool to increase traffic