Cut up the books. Guidebooks are not like regular books that you might read over and over. A guidebook needs to be replaced for each trip with a new updated one. Not only will you save weight, but then you can toss the pages as you move on, freeing up even a bit more weight.
Take the lightest-weight clothing possible. Take all items that will mix and match pretty well so that you can wear whatever is clean. Yes you will get bored but you will be grateful. I avoid anything that's 100% cotton.
Forget cosmetics. No one will care if you're wearing foundation, mascara, whatever. I know a lot of people do it but I couldn't fathom traveling with a hair dryer, flatiron, etc, even though I use them regularly at home. Instead of carrying a tube of sunscreen I use neutrogena's little stick sunscreen (looks like mini deodorant), works great.
Get a little set of lightweight but leakproof travel bottles and bring only what you need in terms of shampoo, soap, conditioner, toothpaste, etc. A lot of people say you can just leave it home completely and buy once you arrive, but I have preferences for all of those things and would rather bring my own, but only as much as I need. If you're not picky then yes buy it there. I haven't tried it, but I have heard that dry shampoo spray works quite well. I plan to try it on my next trip to be able to take less regular shampoo. I'm a big fan of repacking things into as small a package as I can. It helps a lot. I also get a haircut right before I go away because I need much less shampoo (I have inordinately thick hair and need a lot of shampoo when my hair is long).
i believe this is Rick's advice, but it works: when you pack each item, ask yourself, am I sure I will wear/use this multiple times? If not, don't take it.