I mostly play IRL, several times a week, practice against AI, and read the forum and wiki.
I know tons of combos and deck archetypes, and the advanced strategic considerations like being careful when to trigger a reshuffle, the importance of cycling, etc. I win a lot of IRL games against players who don't study as much, but I also feel like I lose more than I should, and I can usually look back and see where I made a mistake.
Some mistakes are obvious. In a Stables game with no +buy, a single-Province engine as quickly as possible seemed smart. Donate was on the board, and after two Silvers and four Stables, I donated down to exactly $8 (SSCCCC) and four Stables. Ten cards, 5-card hands, 8 cards worth of draw, so it overdraws the deck by 3 and should buy singles for three turns dead reliably. Except that I'm an idiot. It's not just that it MIGHT stall after 3 Provinces...it's GUARANTEED to stall after 3 Provinces. It took until that turn where I was staring at that one Copper in the discard pile to realize that. D'oh!
But barring dumb mistakes like that, there are a few other things I'm trying in order to improve my win rate, and I'm interested in opinions about their relative importance. I may have played hundreds of games, but I know there are those who have played thousands. One other note: Even though I play IRL and often in 3- or 4-player games, we always play with 4 Provinces per player, so multi-Province-buy engine strategies are relevant, which usually isn't true when there are only 3 Provinces per player and BM or single buys has a huge advantage.
Here are some considerations:
Point counting
I'm not good at this, and it's really hard for more than two players. Also, Empires makes that miserably difficult! I know that the online game adds point counters, which is a little cheaty. And I do sometimes lose by a tiny number of points, but boy, it's hard to tell if you should buy that VP or go for the pile-out if you don't know who's winning by +/- 5-10 points.
Piling out
Draining piles deliberately is a tricky one. If it takes two turns to pile out, I'm giving everyone else two turns to catch up on VP. Am I far enough ahead? More to the point: When should I be anticipating that the game could end on piles before anyone's opening buy? Certain cards: Haggler, Peddler with +Buy available, strongly imply some piles draining quickly. But I lost a Develop game recently that I would have sworn would pile, and I was even helping it, but the third pile was elusive. Are pileouts something that you usually plan or from the beginning, or simply look for opportunities for towards the end-game, or both?
I've won a few deliberate pile-outs, but I just lost one in which I Salvaged a couple of Peddlers with some +coin into two Colonies before anyone even had a single Colony (they didn't catch on to the Salvager/Peddler thing until it was too late.) I three-piled after that, being the only player with any Colonies...and lost to Keep points in a game with two Kingdom treasures and Platinum (25 Keep points for player 2!) Have I mentioned that Empires makes things really tricky?
Singles vs. Doubles vs. megaturn
Megaturns are rare. I had one yesterday where everyone else was singling, and I happily paid $10 to buy Ball twice and get four more Highways to go with the two I already had. In a Port/Wharf game. Yeah, I know. How was everyone else singling? Like I said, not everyone I play with is super sophisticated. They saw the light when I bought a massive handful of Provinces the next turn. And yeah, I've played HoP decks and other cost-reduction decks.
But the single-Province engine vs. the double-Province engine is the trickiest, partly because they're the most common, and it's often the most important choice. First of all, I should note that with the improvements in card quality, engines are almost always the answer. BM rarely wins, though I occasionally play it, and I'm sometimes wrong. Our group also usually vetoes all cursers, so we rarely play slogs (multi-player curse slogs are the worst.)
But more to the point: Trying to figure out when other players have started buying singles and I should hold out for doubles is really, really tricky. I feel like I'm guessing wrong more than half the time.
What do you think are the best indications that a double-Province engine is going to be faster than a single-Province engine? Assuming there's a +buy (duh) my general guidelines are looking for a trash-two vs. a trash-one, +3 cards vs. +2 cards, and quality of attacks. Trash-twos get you very thin, very fast, and you can get the draw-your-deck, exponential-growth thing going fast. +2 cards just don't get there, except if you can load up on LOTS of non-terminal ones.
Really good sifters usually lean in the direction of singling, but they can also eliminate the need to overdraw by a lot of cards before greening.
You might say that double-Provincing is rarely the right call in a 4P game because there aren't enough actions. But I've lost to it many times because many actions are just that good and you don't need 7 of them. Plus if there's duplicate villages and draw cards, there may be plenty to go around. But I also hate deciding on doubles, getting two double-buys in a row and then having the Provinces go empty and losing to the guy who bought 5 singles.
So how do you decide between singles and doubles? Do you do it on the fly or when planning? What are the best indicators it's going to work?