The biggest issue for me is papers & junkmail. Try to deal with mail as soon as it comes through the door. If you don't have a few minutes to sort it, don't get it out of the mailbox. Have a set place for it. A bills envelope, box or drawer makes it easy to know where to find them when it is time to pay them. Magazines & other things to read should go on your nightstand or in a bag to bring to the dr's office to read there. Opt out of junkmail & credit card offers.
Another huge thing that I have started doing recently is a 5 minute pick-up at 11:55. Just before lunch, I do a quick sweep & put things away. It makes my afternoon so much less daunting! One thing that I need to start doing - that I don't - is sweeping the kitchen floor every night. I am usually way too tired & it feels like it isn't important enough to talk myself into doing.

Pick a room and think about how you use that room. What tasks are routinely performed in the room? Look at the room and find the itms you use to perform those tasks. Are they all in one spot or spread out in the room or even in another room? Your organization will last longer if you plan how you want to use each area of each room and then buy organizers, shelves, etc. to allow for easy access to the things you need. You shouldn't toss anything until you have a plan unless you KNOW you don't want or need that item.

Start by getting rid of things that you REALLY DON'T NEED or use anymore. Take a day and just do that first, and you'll find you have all this extra space to organize the things that are important to you.