What is the best way to get from Lake Orta to Praiano?
The best way is to change your itinerary around so you don't have to spend the entire day traveling. Any option to do that? If not, your best option is to train to Milan, Freccia (fast) train from Milan to Naples, and then Naples to Praiano. Not sure about how best to get from Naples to Praiano. One trick I've used is to find the website of a hotel in your destination city/town and see what they suggest for how to get there. Good luck and happy travels.
By Freccia (fast) train from Milan to either Naples or Salerno. From these latter locations choose the options given in this website: http://www.praiano.org/come_arrivare_a_praiano.htm