How Involved Should The DM Be As A Warlock's Patron?

[MichaelSomething]

If I ever DM for a warlock, I'll text the player bad puns everyday as their Patron.

 

[Lillika]

I try to have each of the characters backstory play a big part in the campaign, sometimes even be part of the major plot and warlock patrons are a very nice way to do this. It's more to drive the story or make interesting decisions and to allow for more character development and roleplaying opportunities. In other words a chance for the character to have a very pivotal impact in the story by the decisions they make and interactions with powerful beings such as their patron. The pc has a huge amount to say, since usually they are ones who tell the gm who their patron is, what he is she is like and such, and then the gm (me) takes that in the weaves a story around that.

 

[Mad_Jack]

I generally tell players when I DM that their backstory WILL be coming up in play, and then ask them just how often, how much, and in what ways they'd like to see that happen. If the character's past is in the past, or they're not interested in being a full-time agent of whatever groups or factions they may belong to, I'm cool with limiting it to the occasional reference to those elements.
For characters with patrons (clerics, paladins, druids, warlocks, etc.) that they'll be interacting with, I try to have it be more of a low-key constant or once-in-awhile flavor thing rather than having them actually hijack the entire party for a quest or something similar - little things that I can handle with narrative description, such as describing how a warlock or cleric who makes a particular ability check might have their success represented by some sort of sign from their patron. Rarely ever as on-the-nose as wondering which path to take through the forest and suddenly a tree falls across one of them, but vague guidance in the form of minor signs isn't uncommon. Gods forbid I ever had a party with a priest of Odin and a Raven Queen warlock - they'd be absolutely plagued by talking crows, and would never know just when one of them might have some bit of information or a mission for them rather than just being chatty, lol.

 

[Sunseeker]

The DM is every god, every patron, every NPC, so really: about as much effort as you want and as much effort as they enjoy.

Few players enjoy additional "oversight" from the DM, so unless you've got your player to write up a specific contract or code or list of tasks, I'd mostly play it hands-off unless the player does something grossly out of line with what a powerful celestial (and therefore presumably good aligned) being would want to see.