Before getting married, my husband spent several years getting rid of most of his stuff. By the time we got married, he literally had one suitcase of clothes, a car, laptop, and golf clubs. As for me, I had shelves full of books, old papers, yearbooks, photos, drums, costumes, snowboard, etc. You get the idea.
So, I asked my then-fiance for some help. Here's what we did.
Phase 1 - Sorting:
My fiancé came over and took all of my possessions and dumped everything onto my living room floor. The pile looked like a big ugly hill. I never imagined that I had so much stuff because when it was all so organized back then. He also brought a bunch of file-sided boxes with handles from Staples, and brought in the large outdoor garbage can (the huge one that you put out on the curb every week).
We then got to work. We had boxes for things to keep, things to give away and the large trashcan for things to throw away. I sorted through everything until the floor was clear.
Phase 2 - Digitizing:
We then went through a digitized everything that could be digitized. Photos were sent to a photo scanning service. Yearbooks, journals, birthday cards, important books, etc were torn apart and put through a fujitsu scanner. For things that couldn't be fed through a scanner, like my drums and gifts that had sentimental value, I took a picture of it and donated it. This was a large project that took several months.
Phase 3 - Detaching:
There were things from phase 1 that I knew I didn't want to keep, but that I didn't want to get rid of either. So I kept those things in boxes in my closet until I was ready to get rid of it. It took probably several months to a year to get rid of some of those boxes. Keeping those items in boxes helped me to detach from them emotionally until I was ready to get rid of them. However, there were some items that even after a year and a half, I still was attached to. So my husband took them out and put them in our living room again so that I could face it. I eventually got rid of those things too, but I took a picture of those items so that I could still keep the memories of what those things represented before donating them.