What to get rid of vs. what to keep

We currently live in a three bedroom, 1500 sq. ft. townhome. The current goal is to get into a much smaller space. So, what do you do with all that stuff? I have always believed that if I haven't touched/needed something for a period of time, then I can part with it. My husband is much more sentimental than me when it comes to personal items. So, we are working through those issues. We have been making progress, but it is slow. I would like to start fresh in a new place, it is so freeing. Then, to take our belongings down to almost nothing will be even better.