XML : How deal with complicated xaml

I am a newbie at C# wpf. I am studying it and still not using MVVM. At the moment though I am already developing some quite complicated (for me) interfaces. I know I will be horribly downvoted for asking subjective or unspecific questions but I need to know how to semplify complicated interfaces. So by looking here Split one big XAML in number of Sub-XAML files

have found (but not implemented yet) that an xml file can be split in several ones.

So my question is: is this the best way to deal (develop + maintain) with complicated interfaces? Any other workaround? Thanx in advance