In general, if you go into a Dominion game with a predetermined mindset like "Silver and Gold is the key to victory", or "Militia is a strong attack", or even "You should buy Provinces to win the game", you will lose terribly when those maxims no longer hold true. Some cards are better than others more often, but in general getting better at Dominion (and having fun at it!) is recognizing which cards are best in each particular situation. This is something you can't possibly memorize, just something you learn by playing a bunch.