From the latest stories that I heard:

Showing up unprepared (none of the requested paperwork, no logbooks)

Not being professional (jeans and a polo are not a good interview look)

Being overly cocky - looking like you will be a trouble maker and constantly in the CPs office.

Not being able to read a Jepp - not knowing basic IFR rules (departure minimums, takeoff alternate, DH/MDA, enter a hold)

Lying on application.

Not being honest.

If you have checkride failures or anything bad, be able to tell what you learned from them.
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Read and study the gouge on aviationinterviews. Be professional. Be honest. Show that you will show up to class with a good attitude and want to be there, will study hard, and do well. If you can do those things, it isn't a problem.

Most people failing the interviews are supposedly prior 121.