public interface IMyService {}
public class MyClass : IMyService {
   UmbracoHelper umbracoHelper;
   public MyClass(UmbracoHelper umbracoHelper)
   {
      this.umbracoHelper = umbracoHelper;
   }
}
public class MyClassComposer : IUserComposer
{
   public void Compose(Composition composition)
   {
      composition.Register<IMyService, MyClass>(Lifetime.Request);
   }
}

// That will register your service with the LightInject DI container, and so it will 
// automatically know to inject the UmbracoHelper class when your class is needed