Autoptimize
I only recently heard of Autoptimize but it’s now one of my favourite WordPress plugins and I’ve now installed it on all of the sites that I manage. I use it to help implement the latest website performance optimisations, such as concatenating and minifying all JavaScript and CSS files, moving all JavaScript to load at the bottom of the page, and minifying the HTML code. On some sites I use it to inline the CSS into the <head> of the document, but that is a more advanced performance optimisation. Its basic options are really easy to understand and can be used the majority of the time, leading to immediate improvements in performance.
BackWPup Free
I use the free version of BackWPup as it allows me to back up the sites I manage to Dropbox in a straightforward way and for free. I tend to configure a daily database backup and weekly full site backups for all of my live sites.
Broken Link Checker
A useful WordPress plugin to have installed as it automatically checks all hyperlinks used across a site and emails you if any are detected broken.
Google Analytics Dashboard for WP
Many of my clients like to see a quick summary of their Google Analytics data in their WordPress dashboard. This is the best plugin I’ve found so far for doing that and I also like how it can be locked to connect to just one Google Analytics account/view.
WordFence Security
I’ve tried out a few WordPress security plugins, but I keep coming back to WordFence. I find it provides suitable protection from hackers without being overwhelming with too many options. I now install it on all my websites.
Yoast SEO
My go-to WordPress SEO plugin as it also generates XML sitemaps, adds Open Graph meta data, Twitter card meta data as well, and Yoast is a highly respected WordPress developer.
ZenCache
ZenCache is my go-to caching plugin due to its ease of use and minimal configuration. I’m sure other WordPress caching plugins might perform better and offer more advanced features, but most of the time I find ZenCache is good enough.