I'd take the Agonizing Blast, Repelling Blast, and Relentless Hex Eldritch Invocations, the 1st level spell Hex, and the Lucky Feat. The Lucky Feat is to re-roll any misses.
That would be 2 bolts, each of which would do 1d10 + 1d6 + 4 damage and the Relentless Hex invocation would allow an additional +4 damage each round. Technically the Relentless Hex damage isn't part of the Eldritch Blast, but it would stack with everything else.
The total damage, assuming 2 hits, would be 2d10 + 2d6 + 12, or anywhere from 16 to 44 HP of damage per round.
Once per turn, you can deal an extra 2d6 damage to one creature you hit with an spell attack if you have advantage on the attack roll. You don’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.
Adding that feat as well might help if you either get advantage or foes adjacent to each other
Relentless Hex is a teleport. Perhaps you mean maddening Hex. And surprise spellcasting is inofficial, isn't it?
In addition to agonizing blast you only have the general ways to increase damage: The hexblade's curse, for example. Or the racial feat of the Aasimar that lets you add your level to damage once per Turn for a minute. You could also get the invocation that allows you to Cast bestow curse and use that to increase damage.
I prefer Spell Sniper feat, Agonizing Blast, Repelling Blast, Eldritch Spear, and Lance of Lethargy, the latter being not especially important and strictly worse than the UA version, Frost Lance. Bump Cha to 20 if possible. That's only 1d10+4 (or 1d10+5 if you can max Cha) per bolt, but it has a range of 600 feet and each hit pushes the target back 10 feet--which, if you have a very kind DM, does 1d6 falling damage. It's more impressive with Frost Lance, in which case you could keep a single enemy with no more than 30 feet of speed stuck for as long as it takes you to kill it. It's also more impressive at 2nd level, when you're outshooting everyone but the variant human fighter (or ranger) with Archery, Sharpshooter, and a heavy crossbow for enemies within 400 feet and a longbow for enemies 401-600 feet away, though you only have Spell Sniper (because of course you're a variant human; hey, min-maxers are good for the old "humans are more common than other races" theory!), Agonizing Blast, and either Repelling Blast or Eldritch Spear at that level, so never mind.
Well, that rambled a bit and I can't seem to find a good paragraph break. Sorry about that.
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1: Get at least 3 levels of Sorcerer. (Probably go 4 if you want to max the damage)
2: Get Agonizing Blast and any other invocations that involve EB . (Probably repelling blast because you want to keep them off you as much as possible with this build)
3: Play as an Aasimar for the racial feat where it adds damage to your first hit, at the amount of your level (so for you +8).
4: Play as a Hexblade, so you get Hexblade's Curse (+ your proficiency bonus for each hit, crit on 19,20).
Ok, so here is how it works:
Round 1: Activate Aasimar feat and Hexblade's Curse (sucks that you don't get to attack but if you stick to the back line, you should be fine)
Round 2 and beyond: You do EB as your action then quicken EB as a bonus action...so that would be 4 shots at level 8. Each one that hits has a +3 damage due to HC and the first one has an extra +8 due to Aasimar feat. So if you bumped your CHA to a +5 by then, then you will have 1d10+16, 1d10+8, 1d10+8, 1d10+8, which averages to 62 points of damage a round if you hit on all of them (and the damage is either force or radiant, least resistant damages in the game).
The caveat: If you went 4 levels of Sorcerer, you will be out of sorcerer points after 2 rounds of doing the quickening. You will have to alternate rounds of EB and converting spells into points as a bonus action with the double EB through quickening. Even on the recharge rounds, you are averaging 35 points of damage if they both hit (which easily keeps up with the heavy hitters of the group).