At the risk of topic drift (avoiding the attention of Ymandragore) i would just like to note that A:RRG is really not all that complicated vis-a-via D&D. Its just different.
To my mind the big three differences are:
(1) you holistically build your character rather than have a class which largely defines you mechanically (instead you will have talents that largely determine what kind of cool stuff you can do beyond a basic attack, and skill ranks which will largely determine how well you do your stuff)
(2) long term, there are no finite resources. Hit points are called Stamina and if you can take a short 5 minute rest then they refresh. Spells, like martial maneuvers, can be used over and over again within the limits of strain (casting too many spells in a short period of time hurts you). So PCs that win a fight go back to "full strength."
(3) initiative is handled differently than D&D. There is a master clock that records "ticks," One, two there...after your first action you calculate the cost in ticks and don't go again till the master clock catches up with you. Every action you take has a cost in "ticks." So its possible to take more (faster) actions over the same number of ticks than someone who is doing something with a high cost. (For example stabbing someone with a dagger is usually 3 ticks. Stabbing someone with a bastard sword is usually 5 ticks. Moving usually costs 3 or 4 ticks. The bastard sword does more damage per hit than the dagger, but the dagger-wielder attacks more often).
With all that said ... The rules for casting without attracting the attention of Ymandragore will vary somewhat between the systems, but
the principles are the same. (A) Better not to be seen casting arcane spells in public. Ever. (B) Having a lie/cover story in place if you are seen is a lot better than nothing. And a good plan B. (C) Hope that the module writers didn't put anything in about Ymandragore.
(sometimes true, too often not)