Applicants for private and commercial pilot certificates have been showing weakness in the following areas.
Lack of knowledge regarding chart symbology. This includes all the symbols, types of airspace, and other details found on sectional or TAC charts. If I open up your local sectional and/or TAC, can you identify every symbol?
Poor selection of checkpoints on cross-country planning. Checkpoints are often too far apart, not based on pilotage – which must be demonstrated, and/or not realistically identifiable from the air. Be especially aware of the need to have several closely-spaced and readily recognizable checkpoints on departure and climbout. The whole idea of the navigation task element is to verify that you can navigate without GPS or any kind.
Reliance on Foreflight's "own ship", "distance rings", "glide advisor", and "breadcrumbs", as well as installed GPS to determine location. If you are planning to use this or any EFB's program in flight, I will require that you turn off those features that displays your GPS position onscreen via an airplane symbol. If you come to the checkride not knowing how to do this, it likely means you have been using position-indicating as a crutch. I will also switch the onboard GPS's moving map screen to another page - traffic, if available.
Slow flight. The airspeed at which you fly this maneuver should be one at which "...any further increase in the angle of attack..." (see PA.VII.A.S3) would result in stall warning. An airspeed greater than 5 to 10 knots above stall speed is simply too fast. This maneuver is usually demonstrated with the airplane fully configured for landing.
Stalls. Both ACSes require the pilot to "acknowledge cues of the impending stall". Practice saying "stall warning", for example, and then recovering from the full stall. See my article on stall recovery here.
Accelerated stall (commercial only). The ACS cautions not to exceed Va, to establish and maintain a 45 degree bank, and then to increase elevator back pressure. If you are too slow below Va, and apply back pressure as you enter into the turn, the stall warning horn (or first indication) will sound before you get to 45 degrees of bank. You'll then have no choice but to recover; since you didn't "establish and maintain the required bank angle, the maneuver is unsatisfactory.
Lost procedures. The “5 Cs” technique is occasionally not taught, and the applicant is not clear on priorities required to maximize chances of determining one’s position when lost. If you don’t know what I’m talking about, check with your instructor.
Touchdown point on landings. All landings require selecting a touchdown point. The most frequent error is landing short of your designated touchdown point (likely disapproval), or needing to "stretch out" the flare in order to try to hit your target (even more likely disapproval).
Emergency approach and landing. Applicants often fail to immediately pitch for best glide (PA.IX.B.S1) and do not have a method for making their approach, instead meandering randomly in the vicinity of their chosen field, hoping to estimate a glide path that will allow them to reach their target and land safely. Guidance in the Airplane Flying Handbook, page 8-26 and 27 is very useful.
Eights on pylons (commercial only). This maneuver is arguably the hardest one of the commercial ASEL checkride, and is mandatory. I strongly recommend you have a few select pylons already picked out where you have repeatedly practiced the maneuver under a variety of wind conditions, since I leave pylon selection up to you. Save these as GPS user waypoints, for example. On the day of your checkride you check the wind, go to the appropriate pair of pylons, and perform the task in a familiar setting.
Suitable pylons should be prominent objects located away from populated areas, such as grain silos, barns, country road intersections, water towers, and other easily monitored objects. Pylons located in populated areas such as housing developments are not suitable.
Maintaining pylon position. The wing tip reference must be precise, and it must be on the pylon – not way above or below it – in order to credibly demonstrate you are maintaining pylon position during the maneuver.
Finally, I the examiner, play no role in pylon selection and I don’t approve or disapprove pylons prior to the maneuver. I also play no role during any phase of the maneuver. You get one chance to get it right, according to the skill elements of the ACS.