A good system is the BUS system, which is:
Is the item?
Beautiful
Useful
Sentimental
If the item in question does not fit in any one of the above categories, then its time for the item to find a new place to live (Sell, charity, recycle or trash).
The hardest part is not convincing yourself something is useful when you haven't used it for 5 years, or that a cinema ticket from your first date is sentimental (which of course it will be, but you don't need a scratty bit of paper to remind you of your past)
I used to have a hard time with binning stuff, and I still have a weakness with clothes (everybody has a weak spot - something the struggle to part with) but for the most part, I am now ruthless, and a clean and organised home is far more beneficial than owning junk that you forgot you owned.
Another system is the one in, one out policy. For every item you bring into your home, one item has to leave. I actually don't find that system all that helpful, but, whatever works for you.
HTH