Competition on the internet has forced us to think of the performance of your website beyond its visual look and we need to integrate different things which can leave best impact on visitors. Here are the quick points to check out.
Creating a check list for UX, Speed of website should be the first point. With different technology, speed of website can be optimized in different ways. Make sure your website has been optimized all suitable ways.
If you are in the service based industry or having a blog, improving Readability of content by modification on its placement, font size, type and color contrast with background makes it more readable.
Many sites and owner don't give importance of developing site search, if you have a large category of products, site search would give you the best result. Make sure it works correctly for the search term entered by users.
What is implemented in your website for dealing with server related issues and unusual errors? Must implement custom pages which direct visitors on what to do next when they face these types of errors.
At last, Must not forget to check your website in browsers and different platform. You can use emulator for different device and browser.
Use of website optimizer and other multi variant tools would be more beneficial to observe user behavior on your website in detail.