I have been using WordPress for the six years; developing using WordPress for five years; and contributing to the WordPress code base for four years. Over the course of this time I have found three things that make WordPress awesome.
With WordPress it is important to update three things: the actual WordPress application, themes and plugins. However, before you begin updating any of these items, you should make sure that you have a current backup. This is important because sometimes these updates don't go as well as planned and you need to restore a previous version of your site. Additionally, you might have made some modifications to your theme or plugin and forgot about the changes you made. Having a backup can help in that situation as well.
There are two pieces to a WordPress site: the database component and the file component. Often people will neglect one of them when backing up their WordPress site. Many backup plugins are written to backup a certain component, but there are plugins that cover both bases. You definitely need to backup both your database and file system; without both, your backups will be useless to you in most scenarios.
There are several things happening on your server that can become bottlenecks as traffic increases to your site. The first bottleneck will be retrieving the data from your MySQL database. The second is trying to execute the PHP code that will ultimately display the content of your site to your end users. New sites with a small amount of traffic might not see these bottlenecks, but as traffic to your site goes up, the efficiency of your server will go down. Standing up additional servers can solve this problem but can be an expensive solution. This is when caching becomes important.
One of the first things that people want to do after creating a WordPress site is to customize it. This is one of the strengths of WordPress, and with the abundance of themes and plugins it is easy to make it your own. As you look to install plugins, I would advise you to follow at these three simple guidelines.