Locate wall studs with a stud finder
Empty the bookshelf
Move the bookshelf into its final position
Mark the anchor points on the bookshelf and wall
Drill pilot holes in the bookshelf frame
Drill pilot holes into the wall studs
Attach anti-tip brackets or L-brackets to the bookshelf
Secure the brackets to the wall studs with screws
Tighten all screws firmly
Check that the bookshelf is stable and does not wobble
Refill the bookshelf with heavier items on lower shelves
Recheck the anchors periodically