Ensure that you install ReactiveUI.XamForms into your applications.
Your viewmodels should inherit from ReactiveObject
Use WireUpControls
Use IActivatableViewModel and WhenActivated for lifecycle
Keep references to your subscriptions
Use disposables to manage lifetime, scope and resources:
Don't use eventhandlers, use the extension methods shipped in ReactiveMarbles.ObservableEvents.SourceGenerator instead
Use your normal Xamarin Forms concepts that you would usually use in Xamarin Forms development, we have some base classes which you should use as they expose observables such as Changed, Changing and Deactivated that can be used for composition.