Don't get all runes, before the temple of Ianna. After temple of Ianna, you can revisit old areas to find the runes, provided that in 5th area (this with the undead and the old fortress, the dragon and the vampyre), you found the secret underground area describing the runes; or you picked one rune already.

Some runes are guarded by high level chaos knights; others are guarded by chaos knights half the level of the others. So, you can kill them and exit the area via the teleporter, WITHOUT picking up the rune. Revisit until you get a level up. After level 22, though, it becomes really long, boring, and actually, pointless.