This article is inspired by an embarrassing game yesterday where I repeatedly failed to Jester good cards away from my opponent because I dumped them with a spy.
A large part of Dominion strategy involves mindless decision-making. You throne room a nobles - cards or actions? A moment's thought tells you that if you're ever going to draw the cards, you should draw them first. Same for minion. From now until the end of time, you will make the decision that way, and after a few thousand games, it stops feeling like a decision. This is augmented by playing on a computer instead of in real life. Learning to autopilot these decisions will free up lots of brain capacity to make more difficult decisions. Moreover, in these two extreme cases, the autopilot will essentially never hurt you.
Sometimes, however, it will. Here's a list of tactical decisions which, while generally true, should not be autopiloted (the reason to avoid autopilot is listed in parentheses after the decision). Please add to it! Note that this isn't a list of strategic decisions (e.g. when can you skip opening sea hag?), which should never be completely autopiloted.
One important thing to keep in mind: each new expansion changes the game dramatically. Decisions you autopilot today will cause significant AP after Guilds and the Dark Ages.
1. Pearl diver sees a junk card, doesn't move it; sees a good card, moves it. (Terminal draw, farming village)
2. Spy and scrying pool dump opponent's good cards. (Jester, swindler, saboteur.)
3. Late game, very close, you don't have 5, buy estate (island, tunnel, great hall)
3.5. Late game, very close, you don't have 8, buy duchy (fairgrounds, farmland a curse into something)
3.75 Late game, very close, you have 8, buy province (farmland , although numerous well-understood strategic considerations here means this shouldn't have been on autopilot anyway)
4. Throne room a throne room instead of a card that draws (mandatory trashers)
5. oracle sees opponent's silver, drops it (If you would leave copper copper, you should probably leave silver/estate).
6. discard the worst cards in your hand to an opponent's discard attack (mountebank, masquerade)
7. have two, might as well get a pearl diver/pawn/... (your terminal draw, opponent's discard attack)
8. play tactician, end turn (do you want to buy a copper? a curse?)
9. opponent plays torturer, curses are out, opt to take a curse (watchtower, menagerie)