Usually the first track I play is: J. Gruska, P. Gordon -The Higher You Rise - Sheffield Track Record. Great recording, although digitized can't touch the direct-to-disk vinyl version.
Otherwise, I usually go with music the listener is familiar with, and maybe throw in a few they aren't. Always interesting to see people trip out over details they've never heard before within familiar songs. I used to date a musician who was a bit "holier than thou" towards non-musicians like myself, particularly regarding the Beatles. I played her a few Beatles songs and watched her jaw drop when she heard instrumental lines, percussion, and bass notes she had never heard in 30+ years of listening on crap equipment. She didn't have a good answer for why I should listen to someone's opinion when they have never actually heard the true extent and fullness of the music.
I've been thinking about making a 1-2 minute spliced demo track of particularly amazing portions of perhaps a dozen different songs - start with light, airy type sounds and progress towards heavier, larger scale stuff. Basically, "here's the two dollar treatment, then feel free to play whatever you want". (I currently have over 50K songs on a USB SSD, almost all are FLAC.)
Michael Jackson - Don't Stop 'Til You Get Enough & Rock With You
Blood, Sweat & Tears - Spinning Wheel
Doors - Ghost Song from American Prayer
Black Sabbath - Behind The Wall Of Sleep & Hand Of Doom
ELP - Still... You Turn Me On
Queen - Get Down, Make Love & Who Needs You
Tom Petty - Breakdown
Devo - Triumph Of The Will
Lipps Inc - Funkytown
Heart - Magic Man
Rickie Lee Jones - Chuck E's In Love
Ted Nugent - Stranglehold
Thin Lizzy - Warriors
Trio - Out In The Streets & Bye Bye
Violent Femmes - Please Do Not Go
White Zombie -Thunder Kiss '65
Yes - Roundabout
ZZ Top - La Grange