What has been working for me is taking it just one tiny thing at a time. I started with one closet. Then, the room that the closet was in. I try to find tips that keep me from getting overwhelmed.
Also, realizing it is a continuous process. I try to grab 2-3 things from each drawer/cabinet on those "donate to vets" days. I did this a lot and had a garage sale early summer.
Next time you are cooking, look in that kitchen drawer with gadgets. Don't you think you could find a few things you never use? Grab them right away, and throw them in the donate bag.
I keep "donate" bags in several areas (laundry room & closets). That way, the first time I see something is too small, it doesn't go back into our space, it goes right into the donate bag.
I also had to get more honest with myself. And reading these mdc threads helps a lot. I struggle with frugality (I could use this someday for free!) vs. wanting to have a designated space for all of our things. Yes, I have thrown away a couple things I wanted later. I decided that is a small price to pay for the simplicity and peace of getting this house in order.
When it becomes too much, I go back to that original space that is clutter free and organized. It feels so nice in there! Once it is clean and organized, it is easier to keep it that way. Yes, it is continuous, but it is a much smaller job.