User blog comment:B214/Talk About What You Want! 3/@comment-28087290-20160407111010

Order of Novels to read:

SLASH/DOG (SD for short)

DxD volumes 1-18

DX 1-2

DxD EX

DxD volumes 19-22

SD introduces the world of DxD, Sacred Gears, The Five Families who control the Sacred beasts (Himejima for example), five characters who appear in DxD: Tobio, Vali, Azazel, Lavinia & Walburga.

DxD of course has all the lore and is the main storyline (SD serves as an introduction while being it's own separate story) but you should read up until volume 18.

DX should be read when u get up to volume 18 to catch up with all the side stories that happen before volume 18 and 19.

DxD EX should be read next as it happens around sometime after volume 18 and before 19 and foreshadows future events of DxD

Then continue with DxD.