1. Separate boxes
Get out 3 boxes or bags. Use one for "keep"/"maybe," another for "give away" and the last for "trash." Fill each up into the desired boxes. And get help from someone if you have trouble letting go. My rule of thumb is if it's been 6 months since I've worn, used, looked at it, it's time to give it away. But if that's too much for you, make it 1 year. Sometimes I even keep things for another 6 months to see if I may end up using it/needing it. But after that 6 months, I let it go if it hasn't been used.
2. Start small.
You may have a large space you want to conquer, but start small so you don't get overwhelmed. I suggest your pantry or laundry room. Those are usually small spaces with not too much going on, but are always in need of a spruce. Once you've accomplished that small space, move on to a bigger area.
3. Pull everything out... well maybe.
Some people say to pull everything out, some say don't. I say do what you want. I tend to not pull every single item out of a closet I'm organizing. If I did this, I would have no room to look through the stuff I pulled out. I do a section at a time. I pull out that section and go from there. Once I pull it out I use the 3 box theory and start filling them up. Once they fill up, I get another box for each area and start going again. Some spaces will take you more than an hour or a day. I spent 2-3 days, when I had free time, to clean out our 3rd bedroom closet. Do some when you have a free moment. Sometimes it helps to walk away and re-evaluate some items you think you need to keep. Get away, get some perspective and come back and start again. You'll be surprised at how much you get rid of this way.
4. "But I'll need this a year from now."
How long have you been saying that? 2 years? Don't you think it's time to let it go? Again, I've done this. But you finally realize you haven't used it, so you probably won't use it. And if you need it, you could borrow it from someone or go to Craigslist or back to Goodwill and pick it up. Be careful not to do that too much, otherwise you'll be back in the same boat you were before. Really consider how much you will use it if you buy it back.
5. Always have a "give away" box going.
Keep this on a high shelf or space out of your way and when you come across something you don't want, throw it in the box. Don't let this box be see-through, as you'll see things that you think you'll want later. When this box gets full, haul it away. And start another box.
These are just a few tips to help you get started. Do what feels right for you, that's the most important thing. You need to feel comfortable with getting rid of your stuff.
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