Sage Advice was a Q&A column in Dragon Magazine, and often provided very useful interpretations of the 1st edition Core Books. Dragon Issue #46 (February 1981) has two nuggets useful for The First Age – the question of familiars for clerics and deity selection for Paladins and Rangers.
Familiars for Clerics
In the Monster Manual, under the Quasit entry, it is stated that Quasits can act as familiars to Clerics. SA confirms that, if the DM allows it, a Chaotic Evil Cleric that has provided long and faithful service may have a Quasit familiar.
I interpret this as meaning that a special variant of the Find Familiar spell then must be available to Clerics at a much higher level, perhaps coinciding with spells that are only accessible by direct grant from the deity themselves – 5th level. The subject of the Clerical Find Familiar then could be the deity servant that previously delivered 1st to 4th level spells to the Cleric.
Paladins and Rangers Selection of Gods
Paladins and Rangers do not need patron gods that are specifically patrons for Paladins and Rangers; instead, the alignment of the gods must be compatible with the classes. A Paladin then would only worship a Lawful Good god. A Ranger however, would worship a god similar to their alignment, but always good.
The Paladin specification of Lawful Good gods only is clear. But what about Rangers? I interpret this as allowing worship of a god that is within one step (but must be a good god) of the Ranger’s alignment. For example, a Neutral Good Ranger could worship a Lawful Good, Neutral Good or Chaotic Good god, but a Lawful Good Ranger would be unlikely to worship a Chaotic Good god. But ideally, the alignments would be the same, for the highest form of communication happens in the Alignment language of the deity.