In a society where design is everywhere, and we could almost say it rules our lives, UX is a terminology that has been adopted by most Web designers and Design agencies worldwide; but even when it is something most professionals in this area have adopted, a lot of them don't really know what UX really means.
UX is not UI
First of all, let us clear the water, UX and UI are not the same thing; UX is part of a process, it's based on testing how the user interact with the product, how the user feels. The whole focus of UX is making sure the product is simple to use and that it works for its intended purpose for its intended user base.
UI means User Interface, it usually is done after the UX research is done, and you already have Layouts created and a solid frame to start creating a design for your users.
So UX and UI work together but are part of different stages on the creation of a product.
UX is a Process
Like most design, UX is a process, but unlike most design, it is more of a science... you'll see: UX stands for User Experience and while we might have some knowledge of basic practices for proper UX design, in most cases UX is something that is developed with time, testing, creating different options testing those options, getting results and taking the proper decisions around what the user needs or wants. Even when the process is properly followed or you make sure to implement the best practices to ensure a great experience for your sites visitors or app users, you might still be able to make tests, tweaks and changes to make the product perfect.
How to UX?
Simple, Ux without User research is not UX. There are different schools of thought around the process for UX, there is the design thinking process, the 6 D, Lean UX, Modern UX, etc All of them with their philosophy and their steps to follow, but all of them have the same base, User Research; the simplest and cheapest way to do this is to create user cases in your mind, check your user base and figure out, age groups, social status, income anything that might help you get a better understanding of who is using your product. Once you have this idea you can create different personas, think about their needs and create a design around that.
You could also test with actual users, the point of UX is testing and making sure your design is centered on the user.
There are a plethora of different terms around Design, User Experience, User Interaction, User Interface, Information Architecture, but you need to have in mind that all of this is part of a process, not something you can just PUT more off in a product. There is no way of just adding more UX to an app, you need to research and create the UX from scratch before you can start to tweak it.