My theory has proven pretty decent this far but the problem is that it's massively unprecise because of all the possibilities. Based on this idea, I've been able to decently well predict some things in newer books, but also pondered tons of (at least to this point) useless ideas. The core idea, though, is that in the series things occur in pairs. Martin really loves to show us something and then turn the qhole set-up around to be as opposite as possible.
There is a pompous king out there? Lol, it's not a king, it's a bastard. See that shabby bastard over there? That's a real king.
Knightly knights turning out to be or becoming monstrous (either appearance-wise or in other ways). And grotesque figures doing the actual "knightly" deeds.
"Bad guys" becoming good and "good guys" going bad. A classic, but I'm sure Martin will use it in the most horrible and delicious ways possible. Also, good intentions leading to horrible or even worse than horrible consequences, cowards being the real heroes etc.
Symbolism turning around. For example: Sansa "the little bird", being naive and religious as the Hound creeps her out. Guess what: there'll be an "evil mastermind -Sansa" and Sandor the Sparrow.
This whole point has lead me to find a ton of connections between characters and events... But also speculating that the endgame of the story is highly likely to corrupt and make the main antagonists from all the "sympathetic good guys" we all have grown to love, and possibly also give us the slimiest, least pleasant "heroes" of all times.
