Usually, when running A/B tests, you simply track the overall conversion rate. Then you test independent elements using multiple versions. At the end you use the element resulting in the highest conversion rate.
Inspiration point: 5 Landing page design changes
John from PPCHero posted an excellent set of landing page tips centered around the idea of simplicity. His #1 tip “Keep call-to-actions above the fold” is common sense advice designers seem to break 60%+ of the time.
Inspiration point: Designing Adwords Landing Pages
David Lindop of Setfire Media offers 7 practical landing page tips. His tips are a mixture of ad copy and design. I’m not a copywriter so this post will focus primarily on the design aspect.
Inspiration Point: How to use ad creative as part of a multivariate test
Ian Lurie suggests that it is imperative to incorporate your creatives into your MVT matrix. I do believe this can be a good idea if you are running a high budget PPC campaign. The only problem I see with this is I usually like to build a relatively high number of landing page specific creatives. It could be a huge pain to incorporate all your creatives into your multivariate test. You may also run into bidding problems going this route.
Inspiration Point: Split-testing email campaigns
A/B testing in terms of web development is traditionally thought of as a function of a landing pages. This is largly because campaigns can run for weeks, months or even years (time is on your side) and most landing pages should have straight forward, measurable call-to-actions.
I find the idea of A/B testing and multivariate testing fascinating. On the surface it may seem like you are just rearranging and adjusting elements on a page to systematically find the best combination. That alone is quite gratifying from a strategic level. I would be more than happy to pursue A/B testing from this angle alone but you also have to consider the human element. Why are certain changes more likely to solicit an action from a complete stranger than others? This data can be used to infer human behavioral patterns and that is what I find most interesting.
This page is a simple collection of A/B testing articles from various sources.