public class PresentationPage : ArcGIS.Desktop.Framework.Contracts.PropertyChangedBase, ArcGIS.Desktop.Mapping.IElementContainer, System.ComponentModel.INotifyPropertyChanged  

{
  //Note: Must be on the QueuedTask
  //Reference a map page
  var mpage = activePresentationView.Presentation.GetPage(4) as MapPresentationPage;

  //Set the map frame extent based on the new camera's X,Y, Scale and heading values
  Camera cam = new Camera(329997.6648, 6248553.1457, 2403605.8968, 24);
  mpage.SetCamera(cam);
}

{
  //Note: Must be on the QueuedTask
  //Reference map page
  var mpage = activePresentationView.Presentation.GetPage(4) as MapPresentationPage;

  //Reference map and layer
  MapProjectItem mp = Project.Current.FindItem("Page name") as MapProjectItem;
  Map map = mp.GetMap();
  FeatureLayer lyr = map.FindLayers("GreatLakes").First() as FeatureLayer;

  //Set the map frame extent to all features in the layer
  mpage.SetCamera(lyr);
}

{
  //Note: Must be on QueuedTask
  // Find specific elements by name
  var ge_rect = page.FindElement("Rectangle") as GraphicElement;
  var elements = new List<string>();
  elements.Add("Text");
  elements.Add("Polygon");
  var elems = page.FindElements(elements);

  //Get elements retaining hierarchy
  var top_level_elems = page.GetElements();

  //Flatten hierarchy
  var all_elems = page.GetFlattenedElements();

  //Use LINQ with any of the collections
  //Retrieve just those elements that are Visible
  var some_elems = all_elems.Where(ge => ge.IsVisible).ToList();
}

{
  //Note: Must be on QueuedTask
  //Select/unselect some elements...
  var elems = activePage.GetFlattenedElements();
  //select any element not a group element
  activePage.SelectElements(elems.Where(e => !e.Name.StartsWith("Group")));
  activePage.UnSelectElements(elems.Where(e => !e.Name.StartsWith("Group")));

  //Select/unselect all visible, graphic elements
  var ge_elems = elems.Where(ge => ge.IsVisible).ToList();
  activePage.SelectElements(ge_elems);
  activePage.UnSelectElements(ge_elems);

  //Select/unselect a specific element
  var na = activePage.FindElement("My Text Element");
  activePage.SelectElement(na);
  activePage.UnSelectElement(na);

  //Select everything
  activePage.SelectElements(elems);

  //enumerate the selected elements
  foreach (var sel_elem in activePage.GetSelectedElements())
  {
    //TODO
  }
}