A simple way to have quick access to your frequent contacts on HTC One M8, is to add contacts to Favorites. To manage your favorite contacts on HTC One M8 do as follows:
1. Open People application and make sure the Favorite tab is visible (Tap the 3dot icon, Edit tabs, mark Favorites option)
2. Now swipe to the tab Favorite
3. Tap the Plus icon on the top, and use either of the options: "Add an existing contact" or "Create a new contact"
4. If you select to choose from existing contacts, then your phonebook opens and you just need to mark the contacts to add them to your favorite list
5. To delete a contact from Favorites, go to the Favorite tab, tap the 3dot icon, tap the Edit favorites, and there you can manage your Favorite list