Start small.. If you look at your whole house and try to start, you will get overwhelmed and quit. Trust me, I'm talking from experience here. So start small, set a goal and don't stop until you reach it. For example:
My dining room wall was at one time lined with boxes. Boxes of books, clothes, misc stuff that just needed sorted, taken to the shed and tossed. So I decided that was my small goal. I got the boxes off that wall. I had a box for trash, for give away and keep. I figure if I don't have a specific place to put it, and haven't used it in the past 6 months, I probably won't miss it. If I really do, I will find another one. Of course there are exceptions to this. I do have a few boxes in the shed of keep sakes, stuff I may never use, but can't give up, they were made by my grandpa, or something along those lines. I just try to be conscious of how much I am keeping. I have 2 boxes of 'household' decor type things. No more than that, I don't need to keep it. So I donate it to our local church pantry, who passes the stuff on to families for free, who actually need it.
That hardest part of de-cluttering is getting rid of stuff. What to save and what to get rid of. I know for me, knowing I was donating it to someone who could use it, was a HUGE incentive. Yes you can donate to Goodwill or a consignment shop, but a church that passes it out for free was even MORE incentive. The people who can't afford Goodwill probably needed it more.
So start small, a specific room or shelf and don't start another project until it's done. Give yourself incentive, like when I get this done I will sit and watch something, or sit at the computer or whatever your relaxing is. If it is a few day job, than take a few days, but just get it done.. You will feel a huge sense of relief and achievement when you do.
So there is tip #1, I hope that helps someone!! lol