Royal Road is decades old.
There has been much progress on both of these sleights since then, although RRC gives a good foundation (and the moves as taught there are more that sufficient for most people, and most tricks).
To learn a lot more about the Pass, get:
1. Richard Kaufman's tape on the Pass
2. Ken Krenzel's tape on the Pass (originally from Videonics, re-released by L&L a couple of years back).
3. Jim Swain's 3 tapes of magic, each of which devotes a section to a couple of passes, and tricks using them.
All of these are good resources for variants, tricks, handling, and most importantly, a chance to see experts doing the maneuver, and what it looks like (or, really, to NOT see experts doing it).
For finesses, see the Steve Draun's book (for the midnight shift), RK's Derek Dingle book (and the DD tape from Jeff Busby, as well as the two Larry Jennings tapes from the same source -- all three have some beautiful demos of the pass), Jay Sankey's 2nd Sankeytized tape, and Gary Ouellet's book The Pass (and companion videotape).
The pass is one move which I learned more from video than books -- it requires timing, and an attention to hand placement, finger position, choreography, etc., which is just easier to learn from video than printed matter.
The pass is a move which requires much practice. You would be better served to learn about as many types and techniques as you can, from as many EXPERT practicioners as you can, and synthesize what you learn into your own style. Your hands are shaped differently than Kaufman's, Dingle's, Krenzel's, and any one else's, so at some level, your pass won't be EXACTLY like anyone else's. But you can learn from each of those teachers.
The best way to learn it is to study with a good practicioner, who is also a good teacher (ask Matthew Field about studying with Richard Kaufman).
Practice some more. One hundred times a day, for a year, isn't too much.
The Double Lift.
See Greg Wilson's "Double Take" video for a survey. See Rafael Benetar's videos for expert handling of a double, that looks like a single.
The best source of help for me was unexpected. I was learning a pushoff Second Deal from Simon Lovell's 1st book. He breaks down the move into steps -- learn the two-card pushoff, learn the take, learn timing. The two-card pushoff turns out to be a great utility move, and is the best setup for a double lift that I use.