all these kats sound pretty spot on. i would add that the more 'daunting' the piece the more time and consideration should be spent on the 'adoption process' , that is, for pieces of music you take on as difficult long term projects, please please please choose the work you most love, connect with, are obsessed with, that you (relatively speaking) cannot grow tired of easily.
understand you can and probably will be spending many months on sections and will probably have weeks (or stretches of several weeks) where it won't sound like anything remotely close to what the finished product will be (think slow hands separate practice, coordination and timing and fingering work throughs, etc.), you really want to make sure you just dont' grow bored witht he whole thing and fizzle out before you can come out on the other side with a playable work.
also, find at least two very very good recordings that have interpretations you really feel are where you wnat to approximate your own expression, put them on a CD or portable player etc. and listen to that thing daily. multiple times daily even. you want your ear to really steer the boat and should treat listening and aural memorization as a sort of 'passive' practice or just part of working it out away from the piano.
memorize. as quickly as possible. priority no. 1, it cannot happen quickly enough. especially with thick/busy textures and large jumps, tricky passage work etc. there is simply too much going on to be 'reading' a lot of the time, the real work actually begins once you have a basic work out of thepiece at a controlled tempo with solid memory. think of it as your price of admission to really start to work things out. a piano professor at my previous school would not even listen to you unless the work was memorized as described above, that is you didn't even have your first lesson until you learned the basics on your own.
hope tha helps, it's what i pretty much go through on my end.