The amazing Scottish guitarist and teacher Matthew McAllister gives a lesson on ascending and descending slurs (hammer-ons and pull-offs) on guitar. This comes via the excellent Siccas Guitars and their constantly updated YouTube channel. Bravo to both. 15 minute discussion and lesson including tips on technique, musical reasons for slurs, and more. Great video with split screen showing multiple angles of the fingers. Siccas really is leading the game as far as online videos go.
Video Link & Source: https://youtu.be/U7axpq-a8AE
If you are looking for technique books I’d recommend my 20 Favorite Exercises (PDF) (simple with videos), or via Amazon Tennant’s Pumping Nylon (simple but very memorable), Shearer’s Slur & Stretch (organized), or Izaonola’s Kitharologus (progressive but very intense).