XAML has a very easy way of implementing the golden ratio and maintaining the correct ratio, no matter the device screen size. This blog shows four different XAML implementations of the golden ratio for a phone-sized display.
Font Awesome 5 is a really great way to add vector icons to your Xamarin.Forms app. Using a graphic font instead of icon images saves a lot of time and effort. Font-based icon sets can be colored and sized quickly without having to update a bunch of image icons in each of your platform projects. This post goes through the steps of getting Font Awesome working in a Xamarin.Forms cross platform app.