I have a long-running warlock character who is probably one of my favorite characters. to cast magic he gambles with demons with his soul and if he draws a bad card he gets possessed for a while to act out the demon's wishes. in this world, the overworld was blocked from the incursion of heaven and hell along with other planes so the demons need a host to access the overworld.

My warlock is a celestial warlock hafling child who saved a unicorn from dying. Now the "elder unicorn" has granted her power to save other creatures from bounty hunters/monster hunters who are killing other unicorns for their magical horns and other celestial creatures to sell. 

Quote from filcat >>

In sight of all this comments, do you think the DM should play the patron?

 I don't see how it can be done any other way.  The DM is the world around the players; their senses, the other people and monsters, the deities, etc....  It seems to me, having had a Warlock player in one of my one-offs, that if you are to run a campaign with a Warlock, the Warlock's patron and backstory need to become an integral part of the DM's story arc (or else the Warlock becomes somewhat weak in character development).  This is moreso than most other classes (can I use the term class or is that like using race?  Maybe job, instead-lol.)  So, to a degree, the campaign and certain adventures need to be about the Warlock and what his patron wants.  Someone else pointed out that clerics and sorcerers can just be a part of the party and pay lip-service to their deity or have a certain flare about them and that is fine, but the Warlock's patron actually wants something from the character!  The idea of being a spy or destroying certain locations important to a particular deity he doesn't like, and so on, requires focus on the Warlock to a noticeable degree in the events of the campaign.

The need for this level of focus on the Warlock character, by default, could make some players feel that character is "more important" than the other characters.  This is ok if you are running a themed campaign (save the world from..., cause the patron to gain power over...), but it's a good idea to discuss this with the other players, so they feel like they are on board with the idea and not being diminished.

Quote from Irianne >>

I'm fond of the class flavor from Warlocks, but there seems to be a consistent pitfall in their RP. Namely: What the hell does my patron want from me?!

There are(/have been) rules or guidelines in D&D for what to do with Paladins who break their oaths. We can assume that the gods of clerics pretty much just want their devotion, but what about Warlocks? If all the patron wants is for the Warlock to act in their name then they aren't thematically different from clerics at all (except for the identity of their patron/god).

A pact should provide something the Warlock wants (spells, invocations, whatever) in exchange for something the patron wants, but we have no idea what this could be. How do you handle this in your campaigns? Obviously the different patrons have different angles, but what are some concrete things the warlock could be doing to make their patron a part of their RP instead of just being edgey sorcerers? And, more interestingly, what sort of repercussions would you consider accepting as a warlock player, or inflicting on a warlock as a GM, if they fail to uphold their end of the pact?

Do they always have to want something from you?  Some entities are satisfied by give out power just to cause chaos. Remember in AD&D1e Orcus would sometimes leave a less powered version of his wand on the Prime, to cause trouble? Others might do it for other reasons like freeing it from a powerful Wizard's spell that forces it to do his bidding. 

You could litteraly just communicate with your patron and ask them what they want.

Quote from DarkCentipede >>

You could litteraly just communicate with your patron and ask them what they want.

 communication is the cornerstone to a good relationship. trust and understanding. no drama. smooooth sailing.

...so, none of that then!

Quote from Kveer >>

The Hexblade and Raven Queen pacts seem to go hand in hand. I am taking the blade, so the pact will probably start with an oath to hunt the Undead, and the followers of Orcus (or anyone else purposefully intending to usurp the Raven Queens position/harness undead legions).

I haven't fleshed it much further than that.

 Hexblade was made specifically for Raven Queen in a previous edition (4e if I'm not mistaken)

My Feylock was basically the secret non-descript agent for Oberon in the Summer Court. I gathered intelligence, spied, seduced and very occasionally assassinated enemies of the Summer Court all while hiding in plane sight as a very minor maiden of the court. When I went to the material plane and joined the party formerly, I had to occasionally perform those same duties against NPCs who were to interested in the Feywild or becoming a bother to the Summer Court.

A pact idea for a future warlock: 

"An entrepreneurial individual hailing from the material planes, seeking strategic investments in exchange for equity stakes in the lucrative sales of their innovative product."

Basically an investment agreement

Quote from Jackleoflanterns >>

A pact idea for a future warlock: 

"An entrepreneurial individual hailing from the material planes, seeking strategic investments in exchange for equity stakes in the lucrative sales of their innovative product."

Basically an investment agreement

 Your patron demands one thing:

Always Be Closing

Pact magic is for closers.

I have an absolute dumbass of a warlock. Like, "INT 7" level of dumbass.

I can only assume that his patron is giving him these powers for nothing but sheer entertainment as the warlock causes all sorts of problems and shenanigans.