The success of a blog depends considerably on help from web hosting, themes, and plugins installed on the site. A plugin installed on your blog should not create any type of malfunction or negative change and should keep everything running the way it was running before you installed the plugin. A plugin should do exactly what it says it will do. Here is a complete list of favorites that I successfully use on my own blog.
In order to run your WordPress site like a pro, you are going to have to install certain plugins. There are plenty of awesome free plugins available for the platform. This infographic by WordPress Templates shows 30 popular WordPress plugins you should be familiar with: