Strong UI/UX, clear messaging and speed.
People generally don't want to wait, get frustrated easily and also just want to understand if your product or service is right for them as quickly as possible.
If you can achieve the above so it loads quickly, they can understand the value prop and how it relates to them almost instantly, and then can navigate their way around, your website will be successful.
Speed and simpleness. It should be able to load in my mobile phone in one second, and I should get a clear idea of what the site is about as soon as it finished loading on my screen.