You've been able to read the prologue through chapter 2 of Skyward on io9, and you could read chapter 3 from a signing, but today, you can now read it all in the same spot and up through chapter 6 on Getunderlined.com. Brandon's assistant, Adam, also says that they will be releasing new excerpts each week until Skyward's release until November 6th.
Adam also said in a Reddit thread that Brandon will be doing a little AMA on Skyward, so leave your questions in that Reddit thread!
Last but not least, if you look at the Skyward pre-order giveaway page on Getunderlined, you can see the map of the world Skyward is set on. If you fill out the form, you can get a free print of the poster, signed by Brandon. You need to have preordered Skyward to get it. Still, that's certainly one way to get people to preorder the book! Nice marketing, Random House. You got me. (Note, this is US only.)
Discuss Skyward in our Skyward Spoiler Board!
Edited by Chaos