Testing Landing Page Optimization using the Taguchi Method can help you to figure out which elements influence visitors to complete an action on your website. The process is relatively simple and has 4 steps.
Step 1: Select elements on the landing page that you believe will influence sign-up
Step 2: Create alternatives for each element
Step 3: Create test 'recipes' that combine these elements according to the Taguchi Methodology
Step 4: Set up and run a concurrent multi variable test
If all this is Chinese to you, then you should read the article called "Landing Page Optimization Using the Taguchi Method". It explains the process with a very good example.
I'd be interested to hear from anyone that has any experience with this!