How to customize Android User Interface ?

Step 1: Download a launcher

Go to the Google Play Store and choose a launcher to your liking. Launchers are apps that modify the Android user interface. These range from the more powerful home launchers (system-level customization) and OS launchers (takes the skin/behavior of other operating systems.
—e.g., iOS and Windows Phone) to theme launchers (easy home screen customization). Your top options include Nova Launcher, GO Launcher, Espier Launcher, Themer, and Buzz Launcher. Try one and see if it fits your needs.

I enjoy themes, so my personal preference is Buzz Launcher. Like other theme launchers, it doesn't dive in too deep into the OS. What Buzz Launcher focuses on is home-screen themes. It provides an automatic setup, wherein you just choose a theme/home screen and the launcher takes care of most of the settings.

Step 2: Choose a theme

Most launchers have a cloud database of themes that you can download and install on your mobile device. A Home pack is a package of home screen wallpaper and app icons. You get access to different home screen styles from tiles (a la Windows Phone) to typography. If you just want to replace your app icons, icon packs are there for you.

Step 3: Set custom widgets

Most launchers offer custom widgets. In fact, many if not all of them support ultimate custom widgets or UCCW and have themes that already use them. These widgets take customization right in your hands because you can actually create your own widgets and the icons that you wish to attach to them. That is, you can install a widget, set actions, customize its appearance, and assign your very own icon.

Many way to customize the user interface of smartphone :

1.Enable the developer option by hitting 7 times on Build number and then customize the animation and UI of smartphone

2.Change the launcher and theme of smartphone

3.Build the image for your own smartphone by downloading the source and repository file from google

You can use any of the Android Launchers mentioned below to customize the user interface of your device.

1. Espier Launcher : Use this launcher if you want your device to look like Apple iOS.

2. Smart Launcher : Its is a free launcher. With this launcher, you can group all of your installed apps and games into six different categories; games, communication, media, utility, internet and settings. Therefore, finding an app becomes an easy task.

3. Launcher Pro : It is a very light weight launcher. Excellent for low memory devices.