I use Gene Hudson's "Instrument Flying Made Easy" for the how-to on scans.
Jeppesen's "Instrument Procedures Handbook"
FAA/ASA "Instrument Flying Handbook" latest edition is far better than previous editions
Tony Kern's "Redefining Airmanship"
any and all of Rod Machado's books
Kershner's IFR book
and the AIM.
You want instructional knowledge, not rote memorization.