Instrument Rating study guide
The eight Instrument Rating test areas
The FAA builds every Instrument Rating Airplane test from its instrument test standard (FAA-S-ACS-8C), split into eight areas of operation. The testing company's bulletin gives each area's share of the test: Preflight Preparation and Instrument Approach Procedures are about a quarter each, so they deserve the most study time. Open an area to see everything the FAA lists for it, with sample questions.
Have a code from your score report, like IR.I.A.K1? Look it up here.