I currently have a changeling celestial warlock about to go to level 3. I picked pact of the tome with ancient secrets and am not entirely sure what spells and other invocations to go with. I'm playing a face-type/support character con artist (faith healer) I have the charlatan background feature but would appreciate some help with what I should do from here.
For cantrips, Minor illusion, prestidigitation, mage hand, guidance all work well. You can also use the friends cantrip along with disguises, in order to get people pissed off at other people.
For rituals, comprehend languages (easier to con people if you understand them), unseen servant (distract people and have it move things), illusory script (hidden messages), augury (omens) can all work.
For spells, suggestion would be your go-to spell. You can convince people to hand over all their money, go into town and spread rumours of your excellence, worship a fake god, or whatever. Lots of fun. Works in combat too, by telling an enemy to get you some holy water (it doesn't matter if he can find any or not, he will spend an hour searching).
As well as the celstial support spells of cure wounds, lesser restoration, and revivify. Fly and hypnotic pattern are also good spells.
At level 4, i would take inspiring leader as your feat. Then focus on +Cha.
And even if it's not your main thing, and even including celestials damage bonus to sacred flame, I would still take eldrich blast at level 10, and agonizing blast at level 11. Putting other things first is fine, but no reason to pass up on easy damage.
It also opens up things like repelling blast, which can be a different kind of support, by positioning enemies for a fireball, or breaking grapples.