If you're looking for strategy about cards to buy, you're not going to find it. This is about playing each hand as well as possible. I've noticed some people making mistakes in how they play their hands. They're small, but they add up fast. So, I figured I'd write a short article about it. I think a lot of people here already know this stuff, but whatever...
I tried to keep this short, but apparently I'm just long-winded like that :/
Using Throne Room/King's Court in an engine.
TR/KC the engine component that you need the most. If your engine relies on TR/KCed cantrips for +Actions, do that. If your engine is in the middle of firing off, TR/KC a +Cards. If you've pretty much drawn your deck, TR/KC a +$ card. TR/KC on a village should be avoided if possible as these effects are much weaker, but if you need to dig further or don't have alternatives then do it. If you only have Villages as non TR/KC actions, then play all but 1 Village and hope you draw into a better action to double/triple. And as always, TR/TR and KC/KC take priority.
Play Golems early in an action chain.
The later you play Golem, the fewer actions you have left in your deck. If you have multiple Golems, you want to make sure as many as possible play 2 Actions. Try to get 2 Actions before playing Golem to guarantee that your chain continues in case you hit 2 terminals. If Golem is being used for +Actions like the TR/KC cantrip scenario above, then play it first.
Watch your reshuffles.
Whenever you would trigger a reshuffle, pause to consider if it's worth losing the cards in play/hand for the next deck cycle. Far too many scenarios to talk about here, but just remember that you're choosing between "play Action, lose cards in hand/play for some turns" and "don't play Action, don't lose cards in hand/play in next deck cycle".
Discard junk (unless you have a plan).
Instead of thinking of Militia as "discard 2 cards", think of it as "choose a 3 card hand". You don't always want to discard junk. For instance, if you have a trasher like Remake/Steward, keep the cards you want to trash. It's not like you're doing much else with your turn. If you don't have much else, then yeah, discarding the bad cards is the right move.
Try to use trash for benefits on high cost cards.
TFBs work terrible on Coppers. The better the trashed card, the better the reward. If you choose Copper to trash, it often means that you've played a terminal trasher that trashes 1 card for little benefit, which is definitely not a good card effect. So, if possible, you generally want to avoid trashing Coppers to cards like Salvager, Remodel, Expand, Develop, etc.
However, there are some noticeable exceptions to this. Apprentice and Upgrade work okay on Copper because they are both non-terminal. Remake trashes 2 cards, which trashes Copper fast enough for it to be worth it. Bishop's VP chips don't increase your buying power this turn, which is why you generally trash Copper to it.
It's okay to trash cards aggressively if you really need to make an important purchase, like Goons or King's Court. On the other hand, if you trash too aggressively, you won't have enough high quality cards left to last in the endgame. You don't always want to trash a Gold or Platinum or Lab, but leave the option open. Of course, if you don't need that Copper and don't have anything better, just trash it anyways.
As a final note: trashing a Curse is considerably better than trashing a Copper, and should be seriously considered. When you trash a Curse, you get an implicit +1 VP. This has exactly the same effect as Bishop trashing a Copper, except without the opponent benefit.
Use cyclers aggressively early game.
Navigator discarding okay hands and Cellar discarding Coppers early is fine. You want that fast reshuffle to get good cards into your draw pile. As the game progresses, tone down how often/how much you discard cards.
Don't give information by playing cards needlessly.
Please don't play treasures one by one, it disguises little. However, if you have to play them one by one anyways (Bank, Fool's Gold), play as many as you need and no more. No point telling people you drew 5 Fool's Gold when 3 is enough for Province. Don't play a Venture if you already have enough $ and might trigger an unwanted reshuffle either.
Play Bank and Horn of Plenty last, play Contraband first.
Bank and Horn of Plenty will give more benefit if they are played last. More treasures in play, and more of a variety in play. Contraband has potential mindgames if you play other treasure first, but I don't think it's worth it.
If I've missed anything, tell me and I'll add it in.
Edit:
Throne Room/King's Court with choice cards.
The options on choice cards can often be split into limiting or expanding options. By limiting or expanding, I mean that the options either let you play more cards or let you play fewer cards in exchange for a guaranteed benefit. Some examples are below.
Minion: +$2 (limiting) or draw new hand of 4 cards (expanding)
Pawn: +1 card/+$1 (expanding), +1 Action/+1 Buy (limiting) (There is an amazing amount of grey area in which options you consider expanding/limiting, so your opinion may vary here.)
Torturer attack: Gain a Curse (expanding), discard 2 cards (limiting)
This matters because when you TR/KC a choice cards, you generally want to choose the expanding option first. This way, if you don't like the results you end up with, you can expand again. You only choose the limiting option if you can guarantee that you will be able to use the benefit. Examples of this would be Minion if you already have plenty of money in hand, Pawn if you have actions in hand you know you want to play, etc.
