Every freshly installed, Ubuntu has no multiverse and universe (two from four) repository enabled. You should enable them manually then Reload to sync the newly enabled repositories. To do this, open System Settings (gear logo) > Software & Updates > check multiverse anduniverse options > Close > Reload > wait until finish. You will need internet connection (approximately 10 MB downloading) to do this. After doing this, you can install approximately 50.000+ packages with Ubuntu Software Center.
2. Enhance Package Manager
Install Synaptic and GDebi. For long term use, you will need GDebi to install single packages by few click. You will need Synaptic for comprehensive install, remove, or upgrade any programs from your system. Ubuntu Software Center is good, but it has no complete control like Synaptic and GDebi.
3. Change Wallpaper & Theme
Ubuntu comes with new fresh wallpapers. To change it, open System Settings (gear icon) > Appearance > select a wallpaper from right panel. To change default theme, you can select it from below the wallpaper options. In this example, we use Radiance theme.
4. Desktop Settings
Few enhancements can be made here. In example, move the global menu back into titlebar in every application. To do this, open System Settings (gear icon) > Appearance > Behavior > checkIn the window’s title bar. Beyond that, you can install Unity Tweak Tool from Ubuntu Software Center to control your desktop completely.
5. Set Privacy
Ubuntu has few new privacy changes such as Lense or application logging. If you dislike that, you can disable that.