Keep plugins and themes up-to-date. Just as you update the WordPress Core regularly, you should also update plugins and themes. Each plugin and theme installed on your site is like a backdoor into your site’s admin. Unless properly secured (vetted thoroughly, updated regularly, etc), plugins and themes are like an open door to your personal info.

Delete any plugins or themes you’re not using. Along the same line of thinking as what’s listed above, getting rid of any plugins or themes you don’t need will reduce the likelihood of being hacked. If you’re not using them, you’re not going to want to update them, so it’s a much better idea to delete them. Read: Deactivating plugins isn’t enough; you must actually click “Delete.”