One of the WordPress plugins that I recommend is called Simple Page Tester. Simple Page Tester is a plugin for doing simple split testing between variations of pages.
What is a split testing, also known as A/B testing, you ask?
A/B, or split testing, is where you create two similar versions of one of your pages, such as your home landing page. WordPress will then randomly serve either of the two pages to your users and then your analytics on both pages will tell you which of the two pages received the best traffic: the best engagement time on page, lowest bounce rate, most conversions. etc.
Then based on the results from both pages, the more effective page of the two is then resubjected to another A/B test, where the design and effectiveness of the page are further refined with another subsequent A/B test with a new variation. This cycle repeats Ad infinitum.
The incremental improvement of the site is always based on user feedback expressed in the form of actions taken by the users. With variations between the two pages, for example, one can determine if a signup form should be placed in a different spot in the design based on which of the A/B test pages perform better between the two test designs.
A good introduction to the concept of A/B testing can be found in this article, A Beginner’s Guide To A/B Testing: An Introduction, by Neil Patel. A/B testing extends beyond web page design into email marketing and direct marketing. For example, companies have long practiced the activity of test marketing products and advertisements in test markets to gauge their effectiveness before rolling out the marketing campaign nationwide using focus groups.
The reason why A/B testing is a critical part of SEO marketing is that this refinement of your marketing message is the dollar cost savings that digital marketing provides. Without this crucial step, the websites, email campaigns, and direct advertising efforts are just wild stabs in the dark with every attempt. True SEO efforts must include this refinement. Almost by definition, without it, it's not SEO; it's just guessing. Don't go that route. Use A/B Testing.
Simple Page Tester, as of May 3rd, 2019, is a freemium product with two premium one-time purchase levels: single site ($59) & unlimited sites ($149). Both have 1-year of phone support.