I haven't played DnD before, but looking through the rulebooks and reading the forums it seems like I have a tentative handle on it.

Next Thursday is the first session.

I want to have a female Tiefling warlock Great Old One patron. She'll be amoral, but not evil ie willing to help the party but with her own interests in mind.

She was a noblewoman betrayed and sold in to slavery where she was bought for a song by cultists who were doing a ritual. Incorrectly as it turns out. They placed her in the sacrificial circle but inversed the runes and sacrificed themselves to empower her instead...the small remains of their bodies formed a small Gazer.  So she's cynical, hates cultists, nobles, and people in general. I'm going flavor vs power and I want her to be fun in a dungeon or out of it.  She can function as social support by charming, stealing, persuading etc...and mind control in the dungeon.  For example I will choose Evard's Tentacles not b/c it's the best spell but b/c it fits my flavor. I want Great Old Ones Cthulu flavor with mindwarping and evil coming from my gorgeous tiefling former noble/slave.

So here's what I have...

Charisma +2

Intelligence +1

As a Tiefling I get darkvision and hellish resistance

I know thaumaturgy, hellish rebuke at lv3 and darkness at lv 5

Skills: Deception, Arcana, Persuasion, and Perception

Languages: Common, Infernal, Undercommon, Draconic

Pact of the Chain: Gazer ie reskinned pseudodragon where the poison attack is it's eye attack. So not especially viable.  I'm considering Pact of the Tome... if you think i should do that give me the cantrips that I'll get with it.

Patron (I'm decided on this)

Awakened Mind

Starting at 1st level, your alien knowledge gives you the ability to touch the minds of other creatures. You can telepathically speak to any creature you can see within 30 feet of you. You don't need to share a language with the creature for it to understand your telepathic utterances, but the creature must be able to understand at least one language.

Entropic Ward

At 6th level, you learn to magically ward yourself against attack and to turn an enemy's failed strike into good luck for yourself. When a creature makes an attack roll against you, you can use your reaction to impose disadvantage on that roll. If the attack misses you, your next attack roll against the creature has advantage if you make it before the end of your next turn.

Once you use this feature, you can't use it again until you finish a short or long rest.

Thought Shield

Starting at 10th level, your thoughts can't be read by telepathy or other means unless you allow it. You also have resistance to psychic damage, and whenever a creature deals psychic damage to you, that creature takes the same amount of damage that you do.

Create Thrall

At 14th level, you gain the ability to infect a humanoid's mind with the alien magic of your patron. You can use your action to touch an incapacitated humanoid. That creature is then charmed by you until a Remove Curse spell is cast on it, the charmed condition is removed from it, or you use this feature again.

You can communicate telepathically with the charmed creature as long as the two of you are on the same plane of existence.

Invocations: Eldritch Sight, Mask of Many Faces or maybe Agonizing Blast mod for Eldritch blast

Cantrips: Eldritch Blast Lv1 Mage Hand Lv1  (if i need something else let me know!!!)

Spells:  I'm considering

Lv1 tasha's hideous laughter, dissonant whispers

Lv2 suggestion, crown of madness, invisibility, enthrall, hold person

Lv3 hunger of hadar, hypnotic pattern, counterspell, dispel magic, gaseous form

Lv4 dimension door, evard's black tentacles, summon aberration, blight

Lv5 dream, hold monster, dominate person, modify memory

lv6 soul cage, eyebite, mass suggestion

lv7

lv8 dominate monster, feeblemind

lv9 imprison, wierd

Should I up my Charisma or choose a feat?

Feats: Metamagic Adept (which i think means i could get an extra lv1 spell slot or use subtle spell or empowered spell), Keen Mind, lucky, eldritch adept(gift of the ever living ones, book of ancient secrets, voice of the chain master?), alert, shadow touched? id get a charisma point and a spell Magic Initiate? i still only have the one spell slot.

Thanks for all your help I'm sure you'll all have ideas that will make my warlock better! :)

Hex is kind of a must have.  It lasts for an hour, you only have 2 spell slots so this is what gives you the ability to sustain good damage over multiple fights,

Because you only get 2 spell slots consider pact of the Tome.  You can still take find familiar, and you can probably reskin it to look however you like. Having ritual casting and more cantrips is really really nice, so you feel like you can do something magical more than 2x.
Cantrips:
Eldrich blast 
Guidance (Tome)
Prestidigitation 
Mage hand
Minor illusion
Mind sliver (vs high armor)
Friends

If you are doing a point buy for ability points, go with 17 in charisma and at 4th level take fey touched to get a free cast of misty step and hex, along with allowing you to have  a few more spells to choose from.

If you are going GOO, consider the play style of getting Repelling Blast and Lance of Lethargy invocations and using that to keep enemies in you hunger of hadar.  Its a fun and unique way to be a great controller and help people in your party with dark vision get advantage, while still doing good damage.

i figured I'd spam eldritch blast in combat and use my spell slots for specialized spells like evard's tentacles for crowd control situation or against a big baddie i'd use tasha's hideous laughter. but other than that I'd like to be a utility/support character for the group and let them dish out the dps.

You’ll find that you don’t use your spell slots very often. With only two spell slots you always want to keep one in reserve for emergencies.