Where is the most cluttered area? Where do you seem to hoarder stuff? Is it your wardrobe, kitchen or electronics?
What's the reason you have all this stuff? Is it because you actually need it and use it on a regular basis or it's just something that you want or wanted at one point.
What I mean by this is sometimes things looks cluttered not because it is a lot but it is simply just not organized. Figure out to see where you can store them based on their daily usage.
Now the unwanted or unused stuff! You have many options when it comes to these depending on it's value you can either sell online, donate to a shelter or just give to a friend or family member.
There are going to be some things that can't be given, sold or donated especially the old electronics with batteries. The rest you can simply dispose. Don't keep it. That's how clutter starts.