I,too, would like to know from the author herself which order these books must be devoured. I have finished the Kings Assassin trilogy any am about to start the Tawny Man trilogy. But I am uncertain as to whether I should read anything else first?
Haha, these books do lend themselves to being devoured! This is the chronological order, and also the order of publication of all her Realm of the Elderlings books, that really constitute one massive story.
Farseer Trilogy Liveship Traders Trilogy Tawny Man Trilogy Rainwild Chronicles Fitz and the Fool Trilogy
Tawny Man can be read straight after the Farseer books, but I would definitely recommend reading Liveships before getting stuck into Tawny Man. Without giving anything away, there are certain links between the trilogies and there is a particular element of the narrative that will be spoiled for you if you go straight into Tawny Man.
The Liveships trilogy is very enjoyable anyway, although it does start slowly. Takes a while to get going, but once it does...wow! You're in for a big treat, and a massive expansion of the scope of the story.
If you're going to skip any series then the Rainwild Chronicles is the obvious choice. They're not on the same level as the rest of the books. I'm not a big fan, though they're not awful. While they do add some extra information to the rest of the story, you won't be missing much if you skip them.
I would also recommend reading The Willful Princess and the Piebald Prince before tackling the Fitz and the Fool books. By no means essential, but it adds a certain something. I'm being intentionally vague.