Well mobs see in a straight line in front of them. The angle of the cone of vision is reduced by higher levels of sneak but not the range so as long as any enemy is facing you, you can't sneak. But that's fine, you don't need to sneak until you're behind them. You just move straight behind them or use the Marksmanship Retreat skill, it's lvl 1 and since you're dex based it doesn't fail, it costs 4AP to move you 15meters in almost any direction, it's a teleport too so you don't get opportunity attacked on the way. You jump all the way behind, or run there, then you sneak and end your turn. Generally due to starting AP being so low, that's all you do the first turn until you have enough to do Haste+Retreat+Sneak(think it's 9 starting AP for that).
Anyway yeah you just go behind enemy lines and hide, so mobs don't turn around. Then next turns you just go behind whatever you want to kill, sneak attack sneak attack etc until you have 1 or 2 AP left then sneak and end turn hidden so again mobs don't turn around.
There's very few situations where I get hit on my rogue, charm is the messiest when you charm a mob and it turns around to fight whatever you're next to because for some reason you can't sneak in front of charmed mobs. If you get caught in a bad spot you can invis then sneak(it doesn't break invis and since you're invis you can sneak 100% of the time).
If you get the 5sneak right away using the vendor reload trick, Rogue is really strong right from the start, even before Glass Cannon. It's extremely AP efficient and it never misses(if you have Heartless trait that is) even on hard mode, even on skeletons daggers still do decent damage with backstabs+sneak attacks.
There is one skill book somewhere it seems, but only one? Any other ways?
