I would go:
1. Interview with A Vampire
2. The Vampire Lestat
3. Queen of the Damned
4. Tale of the Body Thief (though I skipped this one)
5. Memnoch the Devil (of course!)
6. The Vampire Armand
6. Pandora
These are the ones that are loosely related. Do NOT read Queen of the Damned without reading The Vampire Lestat first.
The rest of them (Servant of the Bones, etc) are not really related, so you can read them at your convenience.
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