Measuring all of your applying is key to having effective landing pages. You can choose A/B testing to measure the user experiences from many aspects. You should save the different applications you make by keeping other variables constant.
For example, you can make color test and want to decide the optimum button color that provides high conversion rates. In another test you can change the banner type and see the change in conversion rates.
To measure the success of your actions, you can use some metrics like page view, conversion rate, bounce rate, clicks, leads… You can decide your optimum landing page and increase conversions. In this way, you may decrease ads costs too.