There is no easy way to answer this as a lot of it depends on the class and specialization you use. For example, if you are an assassin rogue, you'll notice that your passives give you things like guaranteed crit when attacking from stealth, and you restealth if you manage to kill an enemy. This makes it so you don't have to invest so heavily into critical hit chance, and can instead focus on critical hit damage, so in this event, I focus more on dexterity and crit damage. What I am saying is that the passives you choose for your class and spec will be a determining factor on what best suits your needs. If you are a 2 hand warrior, you'll want armor pen so those hits strike a bit harder, depending on spec, I shoot for 50ish percent, which isn't too difficult to achieve via your weapon and possibly a 20 percent armor pen ring. The rest, as the above poster mentioned, as a rule of thumb, I tend to go nuts on crit chance and crit damage when possible. Same for mages usually, best achieved by putting them in medium armor (via using snoufleur skin) and focusing on cunning. Now as to how much to have, that is personal taste. My current knight enchanter has like a 70 percent chance to critical hit at the moment, achieved via using sturdy prowler armor with lurker hides stuffed into the utility slots, and she has a seer staff which gives you offensive leather slots to stack up more crit and some crit damage.