Here is a list of essential task that you should do after installing your wordpress blog.
1. Create a Favicon
2. Put keywords in your URLs
3. Create an XML sitemap
4. Register your site with Google Webmaster Tools
5. Create a Robots.txt file
6. Make a contact page
7. Install a spam filtering plugin
8. Install a database backup plugin
9. Install Google Analytics
10. Ensure good page titles with an SEO plugin
11. Install a related posts plugin
12. Add Subscribe to Comments plugin
13. Add social networking and bookmarking buttons
14. Install a cache plugin
15.Add Google AdSense Code if you have to monetize your blog.
I hope this checklist of essential tasks will help to everybody and newcomers.