I like to recommend the basics-
First, add in the Silents wherever you want. I suggest doing so after seeing the basic Universal classics. The essential silents are Phantom of the Opera with Lon Chaney, Nosferatu & perhaps The Cabinet of Dr. Caligari.
The Universal Must-Sees (1930-49?):
Frankenstein & The Bride of Frankenstein (these must be seen as close together as possible), both starring Boris Karloff
Dracula, starring Bela Lugosi
The Mummy- Karloff
The Wolf Man- Lon Chaney Jr.
after those, add Frankenstein Meets the Wolf Man (the first monster fight movie) and Abbott & Costello Meet Frankenstein (the first big monster comedy).
Then the Hammer Studios era (1958-1970s)~
Horror of Dracula- Christopher Lee & Peter Cushing
The Curse of Frankenstein- the same
The Curse of the Werewolf- Oliver Reed
Phantom of the Opera- Herbert Lom
Brides of Dracula- Cushing
There were a lot more Hammer Dracula & Frankensteins, also some Mummy films, but those are the cream of Hammer.
The best of American International Pictures (1960s)~
The Masque of the Red Death,
The Pit and the Pendulum,
The House of Usher,
Tales of Terror (trilogy),
The Raven (horror comedy)~
all of the above starring Vincent Price & based on/inspired by Edgar Allan Poe
The Haunted Palace (with Price),
The Dunwich Horror (starring Dean Stockwell)~
both based on the writings of H.P. Lovecraft
I also recommend-
the original B&W Night of the Living Dead
a European B&W listed as either ‘Black Sunday’ or ‘Mask of the Demon’ starring Barbara Steele
a US B&W that looks like it was made for $100 but is total nightmare fuel- 'Carnival of Souls"
Those three can be watched for free on the Net, probably at YouTube
Other Vincent Price classics-
The Fly
The Abominable Doctor Phibes
Dr. Phibes Rises Again
Theater of Blood
The original The Wicker Man starring Christopher Lee & Edward Woodward
More modern horror-
the original 1970s Texas Chainsaw Masscre & its superior sequel TCM II (starring Dennis Hopper)
Poltergeist
the original Halloween & II starring Jamie Lee Curtis & Donald Pleasance
Nightmare on Elm Street
Return of the Living Dead & ROTLD II
The Blair Witch Project
and when you turn 18…
David Cronenberg’s The Fly
Re-Animator
Bride of Re-Animator
From Beyond
Basket Case
Brain Damage
Henry: Portrait of A Serial Killer
The Silence of the Lambs
House of 1000 Corpses
The Devil’s Rejects
Rob Zombie’s Halloween & II
The new Texas Chainsaw Massacre & TCM II