Just a quick tip I learned today trying to change my audio inputs.
Note you can only rearrange the Apple supplied Menu Bar icons such as AirPlay, Bluetooth, Wi-Fi, Audio, and Power; third-party Menu Bar icons are not moveable.
Hold down Cmd and click on the icon to move, drag to it's new location and drop. Simple as that! You can see in the screenshot below that I was moving the Wi-Fi icon.