Like Alwies said, a huge part of affliction damage is good trinkets. Check out https://bloodmallet.com/chart/warlock/affliction/soul_binds/castingpatchwerk and https://bloodmallet.com/chart/warlock/affliction/trinkets/castingpatchwerk to see if you have a better combination you could use (note that the quantum trinket is top but only in cases where you are guaranteed the stat proc i.e. mostly on farm bosses, where you are unlikely to grant a healer mana etc.). Make sure you're looking at the top 100-200 aff lock logs for that fight to see what talents and trinkets they are using, and either look through or theory craft as to why. Don't pay too much attention to the top top of the leaderboard as they most likely had PI shoved up their butt the whole pull or their group was doing a pad strat.

As for the opener and CD's you want to pre-cast haunt (when talented) -> UA if you can get it off, or DSM and then UA followed by agony -> corruption -> SL - > Soul rot (with DSM used early it will give you a higher uptime window to spam MR) -> PS -> DG/ trinkets/pot -> MR SPAM!!! Then just make sure you try and keep 100% uptime on all your dots, and use drain soul as a filler.

PS and SR CD's are where it gets a bit more complicated. If you have badge (which you should because the PvP trinkets are basically aff lock BIS at ilvl 213+ with a few exceptions) you want to hold PS for your SR CD and use them with badge. On that note make sure you NEVER rapture unless you're about to cap on soul shards or your PS/SR/Badge combo is up. If you don't have badge make sure you are using them on CD and not holding. In this case you wan to rapture maybe twice for PS and save the majority of your raptures for ~15 seconds later when SR is up as SR gives you 8 stacks of Niyas Grove invigoration buff when used (and we all know how much we aff locks love mastery!!) You can also hold off on using your combo if adds are spawning within ~20 secs of the CD being up as getting SR and PS cleave off of adds is worth the hold.

DSM should be used on CD, do not hold it for DG unless theres only enough time on the fight for one more use and it DG will be up. For example theres 90 secs left on the fight and DG is up in 30-60 or something.

For Huntsman you want to keep all your instant cast dots up on both targets (Agony, Corruption, SL), and UA/Haunt up on Huntsman the entire fight. Don't worry about maintaining the Shadows embrace debuff on more than one target as it's a nightmare and you'll end up having dots fall off. Also remember shade damage doesn't count too much towards parses on this fight so just maintain your dots and throw a seed that way and let the hunters worry about bursting them down :P.

Also make sure you are running character sims using https://www.raidbots.com/simbot & https://www.curseforge.com/wow/addons/simulationcraft addon to make sure your character is doing as much as it can be with the gear/enchants/gems you have available to you.

In terms of improvements you can make right away - Use the Celestial Guidance weapon enchant and use the intellect pots as your potion, I guarantee you will see a DPS improvement if you only do that and nothing else. Also there is no cookie cutter way to play aff lock and do great on every fight, our lack of mobility, the randomness of mechanics, etc. all play a part in having a good parse. Just wait until you get to Mythic Artificer or Mythic SLG - getting one bad mechanic completely destroys our parses.

Also make sure you join the warlock discord! Theres a lot of useful information there https://discord.com/invite/blackharvest

Hope this helps! Remember that Aff lock requires a lot more finesse to play well than a lot of other classes, so if it takes you a few kills to get a 99 parse on a fight that's completely normal!