Class Tree Example
For the Class Tree, you will find a reasonably rigid setup regardless of the situation. Seal Fate is a staple for Assassination, and the left side of the tree straight down plays into our damage very nicely. Not only is our Raid Utility on that side of the tree in the form of Atrophic Poison, but as you travel down and get Virulent Poison and Deadly Precision, you get a nice damage boost. Vigor into Leeching Poison and Seal Fate round out the left path. Thistle Tea is taken in Raid Encounters but can be skipped in Mythic+, where energy is more abundant.
The next path to look towards is the center. This is where many more generalized talents are, which are helpful in various situations. You can pick whatever Utility you would like to get there, but in my opinion, pathing to Cheat Death is a must. Your goal should be getting down to Echoing Reprimand and Resounding Clarity at the bottom of the path, picking up some nice passives on the way. These include Thief's Versatility, a range increase from Acrobatic Strikes, and some passive healing through Recuperator. Going down the middle path, however, also opens up Alacrity and the choice node between Marked For Death and Deeper Strategem. In every piece of instanced content, I recommend taking Deeper Strategem for the finisher damage. Marked For Death is noticeably worse, but it can be picked if you can guarantee very frequent resets. This typically requires staggered adds multiple times every minute, which is a rare situation to find yourself in.
The right column of the class tree is nice for the first few rows, even just for Shadowstep and Tight Spender. After that, there's not a lot of good things I can say about the path. Nightstalker without Shadow Dance is not a DPS gain since the Nightstalker benefit does not attach to damage over time effects for their full duration anymore. Improved Ambush is good, but with its position behind Nightstalker, it turns into a 3-point talent, which just is not worth it. It gets worse with Soothing Darkness being of little value, followed by Find Weakness, which does not affect a large majority of Assassination Rogues Damage. Poisons and Envenom do nature damage, which ignores the target's armor. Bleeds such as Garrote and Rupture also ignore the target's armor. That actually leaves very little from our kit, which is affected, mainly generators and auto attacks. Shadow Dance is an interesting talent all on its own. In theory, it's a good burst option, but there's some issues with its design. In single target you would want to use it mainly to Ambush instead of Mutilate, which isn't nearly as large of a gain as other capstones such as Echoing Reprimand or Thistle Tea. The place where Shadow Dance shines is in AoE and Mythic+, where you can get 6 empowered garrotes out every minute. That makes Shadow Dance on its own really good! Except you still have to invest 7 mostly useless talent points to get to that point after Tight Spender, and that's simply not a cost you could ever justify. You lose way too much going Shadow Dance, and the only thing you get out of it is Shadow Dance.
Dragon-Tempered Blades - Single Target Raid
This build revolves around a more passive playstyle with Dragon-Tempered Blades, and less of a burst/execute focus. Dropping Exsanguinate is very detrimental, but you will want to grab a point in Improved Poisons instead.
Dragon Tempered Blades - Cleave Target Raid
For Cleave, I suggest taking this more passive option with Dragon-Tempered Blades again. However, this time we opt into the left side of the tree for Crimson Tempest and optimize some routing to get us back to Blindside and Zoldyck Recipe.
Dragon-Tempered Blades+Indiscriminate Carnage - Mythic+
This is our best build in Mythic+ and utilizes a lot of talents together to form a cohesive group of utility and damage. The main thing to notice is that while we do take Indiscriminate Carnage, we also take Dragon-Tempered Blades. This is because of the drawbacks of each. Indiscriminate Carnage is very weak in single target and suffers a lot on bosses. We balance this out by taking Kingsbane through Blindside, which connects fairly smoothly through our AoE talents, Crimson Tempest and Flying Daggers. Zoldyck Recipe is also very strong in Mythic+ and can help on hard bosses as well. Overall a very complimentary set of talents. If you wish to drop Exsanguinate, you should do so by taking Master Assassin. This still allows you to take Iron Wire, which is our most powerful piece of mythic+ utility and should ALWAYS be taken.