Switching between a standard and mobile theme is probably the easiest way for most WordPress developers to create a mobile web experience for their users.
Although there are a lot of different ways to go about this, most like to opt into a plugin to do the job.
To save a lot of time and effort…

Just use ‘Any Mobile Theme Switcher’

Any Mobile Theme Switcher for WordPress is without a doubt the absolute best way to switch between mobile and standard WordPress themes.
This plugin is not only insanely quick and simple to set up, it does exactly what it is supposed to do without issue.

Features include the ability to select which theme to display on different devices including Android tablets, Android phones, iPhones and iPads, Windows mobile devices and more.

To utilise Any Mobile Theme Switcher, just create a WordPress theme as well as a mobile variant, then choose which devices should view your website as a mobile version. If need be, multiple mobile themes could be used to target multiple platforms and devices.