[...] When you Solo play Assassin, you make plenty of observations about your environment and how the groups of mobs are positioned or moving, etc. You'll also have to learn to be patient and watch your chosen "mark" and make your deadly strike count.
It's generally not advisable to blindly rush around and aggravate large mobs; since you'd be potentially losing your valuable Sneak Attack bonus, when more than one monster tries to pound you.
An Assassin will typically separate a single monster from the large group via Bluff, or know your limitations on how many mobs your Rogue can handle toe-to-toe if it goes pear-shaped. You won't get Assassinate until: Level 12. So before then you should be learning how to approach mobs without being detected by the main group – picking off lone stragglers or learning how to separate them.
Learn to thin-out and control dangerous groups; so you don't get hemmed in, as that can lead to a fast and stupid death...
You should make good use of Sneak as it will allow you to get very close to your specific target (choose which foe you want to fight) in many cases and dispatch them more efficiently, without alerting the whole dungeon.
If you're playing in a group you typically have the luxury of the other players generating the aggravation, still you want to be flanking and backstabbing. Albeit in groups you don't typically need to be moving in Sneak that often once mob combat has commenced. You still do not want aggravation from the mobs if you can help it. Since you are meant to deal swift massive 'Sneak Attack' damage, and not waste your time trying to slowly wear down an opponent with endless puny swings.
I exclusively play Assassins when at Epic and the majority of the time I'll solo them.
I'm not really into the hardcore "minimum kill discreet stealth runs" I tend to clear all the mobs rather than leave them living. However, within the '
R.O.G.U.E Part Quatre: Call for Stealthy Players!' thread, I obviously wanted most of my kills being provided via Misadventure, [
Post #375].
Don't spend too much time in Sneak mode; when in within a group, which is very inefficient. You should be able to get plenty of kills and Sneak attack damage within a group situation and also regularly Assassinate. That's assuming you are doing a quest level difficulty you can handle.
If you've never dealt with traps before then of course you will be a little slower. Albeit you should be still getting plenty of melee action, and you should be able to help debuff some bosses.
The Sneak [button] now seems to be mostly just cosmetic with regards to Assassinate. Because you can stroll up to your amoeboid Ooze opponent (that has no vitals and already can sense you). Aggravate it; get it swinging wildly at you; begin using /dance to annoy it more... Tell it a joke about /death count, ask it "Do you come here often?" ...
Then simply Click Sneak, it will likely miss you, and then hit Assassinate resulting in; a pretty much dead Ooze! ...