These are some of the findings I've  discovered through many years of testing in a bid to retain this valuable  knowledge and avoid past mistakes, I'm sharing them with you now. You're welcome : )
Some key testing findings.....
1. Place  Call-to-Action on bottom right. Always. 
2. What are the  3 main features/benefits – ‘unique value proposition? Now are they immediately  obvious on your page? No? Put them there.  
3. Do you have  credibility indicators for your website; testimonials, reviews, awards, stats?  Use them. Ideally as secondary content. By that I mean placed in content that isn't a lead up to your main Call To Action but in content below or to the side of it. 
4. If you can  drive people to a product page instead of a hub/portfolio page, do it. 
5. Avoid  additional links on your page. Generally speaking these are just leakage points. Customers will use  them given the opportunity. 
6. Strongly  differentiate between products where they are jointly visible on the same page. 
7. Is your copy  generating any fear? If you have to throw up a negative messages relating to your product such as "this *** if used incorrectly will kill you" consider the tone of voice in  which you do it. 
8. We’re not  selling features, we’re selling solutions to customer problems. Need led  propositions works. Always. 
9. White space  can be used to make a page look less ominous. Too much and it makes it look  amateurish.Get an eye for balance.
10. Too much of  one colour on a page leads to information blindness. Avoid the Sea of Red/black/yellow. 
11. Anything  that rotates or animates tends to draw focus to your static secondary content.  Place your proposition in the static content. 
12. Ensure  continuity of look & feel in the journey. You’ll increase drop-out if you  ask a customer to go through multiple brand look & feel experiences. Continuity and flow.
13. Your existing  customers are considerably more likely to buy from you than new customers. Differentiate  between the two segments whenever possible. Use a sense of loyalty.
14. Remove  choices. Yes you should always support multichannel but be aware if you offer a  CTA to offline channels you are generally loosening your online sales funnel. 
15. Understand  where the visitor came from. If you said something in a PPC Ad make sure it’s  reiterated in your page front & centre. If they came from a  Partner/Aggregator  they are a ‘hotter’ lead and need reassurance that you’re up  to the job of giving them a solution to their ‘need’. 
16. People  don't read on the Web. Study after study has shown that less content on a  landing page leads to higher conversion rates. Ruthlessly edit your text down to  simple headlines and short, bulleted lists. Cut out the self-promoting marketing  speak that people won't read anyway. You can link to detailed information on  supporting pages. 
17. Despite  what many people say there IS a page fold. Be aware of it and if it’s crucial to  the user journey and the value proposition it SHOULD be above the page fold. 
NEVER SECOND  GUESS THE CUSTOMER. TEST MULTIPLE EXPERIENCES & THEORIES. LET THE PUBLIC  DECIDE WHAT WORKS. 
Happy testing : )