My best preflight briefs came from my ex-WW2 instructor, once Catalina pilot and later Cranwell QFI. After 55 years I can hear his gentle tones as though it was yesterday.
Before spinning the Tiger Moth from every attainable attitude: This is a very safe aeroplane, it can only just kill you. We're going to ensure that it doesn't.
Before crossing the Irish Sea: You can go solo after you take me into cloud and fly to my instructions for 15 minutes. There's no horizon 20 miles out on hazy days. (On my second crossing there wasn't, and I was very glad of my instrument training long before the IMC rating)
On the 1950s ADF system little different from his Catalina days: Never trust a black box, remember a black box has no fear.
My best post-flight briefing came from the CAA examiner after I quite rightly failed my first IR test for climbing 200ft into controlled airspace before clearance – I was flustered after being unable to break into the busy London RT. The rest went perfectly, then I was given 20 minutes of the finest instruction I have ever had. Next attempt was easy. Thanks again, Capt. Gunn, if you're still on frequency!