I just started a game not too long ago and i want to make the right decisions with my Hexblade Warlock.
the party consists of me the warlock, druid, ranger & a paladin. I am the only one with darkvision, so i would like to take advantage of that and right down that rabbit hole.
I want to be casting darkness on enemy's or myself and fighting them within it, but i'm not to sure what the best build would be. 
Sentinel is 100% something i want to get to keep people in the darkness spell, however I don't want to get polearm master as the paladin already has it and i want a bit of variety with the party i'm in.

Below is all the stats and info. 

Drow Half-elf, Hexblade Warlock, level 2
Background - Charlatan
Str    8   (-1)
Dex  14 (+2)
Con 14 (+2)
Int    12 (+1)
Wis  12 (+1)
Cha  17 (+3)
Skills - Deception, Intimidation, investigation, Slight of Hand

so what to you guys think, I am going to be the face of the party for the most part, but i do want to be able to do some cool stuff when in combat as well, just not sure what feats to get.

currently i am dual wielding 2 short swords and casting EB until i get the darkness spell.
100% going pack of the blade

Darkness on yourself once you get the Devil's Sight Invocation. No failure chance and hard to dispel.

I would also consider the Grasp of Hadar Invocation if your point is to keep them near you.

Shieldmaster is a great feat if you plan on using a shield. Sentinal is always a good pick as you have pointed out if you want some control.

This last one is a stretch but if your DM is not following the STR requirement for armor you could consider the Heavily Armored feat. You get medium and shields from Hexblade and having the option of plate+shield+darkness is killer. I used this on my Lockadin to great effect: https://www.dndbeyond.com/profile/Devolnu/characters/18752174

Darkness targets points, not creatures, so you can’t cast it “on yourself” to have it follow you, positioning will be important. 

Without Devils Sight you aren’t going to be able to make Sentinel OAs or Warcaster OAs (EB+Grasp of Hadar+Lance of Lethargy), since you need “a creature you can see.” Just remember that garden variety Darkvision isn’t enough. 

Rather than Sentinel or Warcaster, I’d maybe suggest you bump Wisdom up a little (ASI +1 Cha and Wis) and multi monk, way of shadow. It will give you more ways to cast Darkness, more ways that Darkness helps you, and Stunning Strike on an OA and/or your own round’s attacks will keep targets locked down in Darkness as well or better than Sentinel. Short swords are monk weapons, so very little about your play style will need to change, other than taking off your armor.

You have said your own downfall. You are the only one with darkvision, and not even magical. Darkness will make the pally deal less damage, blind everyone etc. I would instead go the root of pinning people down, moving them etc. Helping the druid to cast entangle etc then place down a big aoe and ask pally to throw javelin, ranger to longbow etc. Much better than this current build. Darkness is always useful for running though. Remember you can get into combat to, and don't be afraid to accompany the pally on killing disadvantaged enemies (prone, restrained etc). 

Quote from Chicken_Champ >>

Darkness targets points, not creatures, so you can’t cast it “on yourself” to have it follow you, positioning will be important.  

Darkness can be cast on an object. So the "point/yourself" can be your dagger. You can even cover up the source of darkness just like Light.

Woof, I gotta start reading the second paragraph of spells :p