i would say you tap an open note by tapping (for example) the 7th fret then pulling off to an open note, i dont see any other way you can do it.
as for tapping 2 notes at once, yes you do need alot of practice, as strong as your fingers may be from finger picking, your going to have to build them up again!, it also a good idea to strengthen your ring and pinky finger if you really wanna be a master tapper
finally tap whatever sounds good!, most people use appegios there are a few other patterns for tapping, i'm sure the book will show you some