Here is the best WordPress Plugins which i am using in my site.This are all free and you can download them from the official WordPress plugins.You should use those plugins to improve your blog efficiency.
Yoast’s WordPress SEO plugin is the google ,bing,yahoo and other Search engine optimize plugin.It will Improve your SEO.
best guard against comment spam for WordPress blog.ITt Automatically checks all comments and filters out the ones that look like spam.
This plugin will generate a special XML sitemap which will help search engines like Google, Bing, Yahoo and Ask.com
Jetpack Customize your WordPress with with Custom CSS, Carousels, spam-free Contact Forms, Sidebar Widgets, Infinite Scroll, and Tiled Galleries.
It logs the IP address and the exact date & time when a user is trying to log into your WordPress and also keeps track of unsuccessful login attempts.
This Plugin will help you to add Adsense ads on your WordPress blog.It’s very easy to Manage your ads quickly and easily through a point-and-click interface.
This is possibly the best caching plug-in for WordPress and it will definitely help improve your site’s page speed score.
Simple but effective plugin allows you to extensively clean up your WordPress database and optimize it without doing manual queries,
A simple and easy way to test your theme for all the latest WordPress standards and practices. A great theme development tool!
Use the Debug Queries plugin plugin to determine which MySQL queries are taking more time to execute and thus slowing down the blog.