The things that actually cause trouble early on — reading the weather, deciding whether to go, and walking into the checkride knowing its shape. Free, no signup.
A METAR is the same eight things in the same order, every time. Here's the order, what each group means, the trap in the sky-condition line that catches nearly everyone, and the flight-category thresholds — with worked examples.
Legal minimums keep you out of trouble with the FAA. Personal minimums keep you out of the accident report. Starting numbers by certificate level, what to set beyond ceiling and visibility, and the one rule that has no exceptions.
The paperwork that cancels checkrides before they start, how the oral really runs, what the ACS tolerances actually are, and what a Notice of Disapproval means — which is much less than you think.