If you have some time, have a look at the Marie Kondo thread and the Minimalism threads - there are links throughout the threads, as well as tips, advice and encouragement. Marie Kondo has a book, but you can also find things from her and other minimalist writings online - it can be very useful and motivating in starting to work out how to get organised, getting rid of useless things, only having things you need or love, etc.
From my personal experience, I recommend looking at anything stored that doesn't get used much/at all (in cupboards, drawers, sheds, wherever) and making a quick analysis - if you don't use it, do you love it? Or just nervous about "what if..."? If you don't love it (ie not precious, hugely sentimental, beautiful) then it goes immediately.
Don't think about the value of things or guilt, like "it cost £50" or "friend A got it for me". The money is gone already. Friend A won't know, you haven't even been using it anyway.
I like to work in zones - I sorted out my bathroom,first, because it was easy and having one finished space spurred me on. However some people like to do categories, like all books, or clothes, and so on.
Don't let it get you down, as being deflated won't change anything. But do enjoy each time you make a difference, big or small, and that will make it all easier.
Avoid buying things just for the sake of it, let it be for real utility or love.
You can try talking to relatives about what they buy you and DC, I know plenty of people on the Minimalism thread have made headway in avoiding an onslaught of tat! But I don't have this issue so much so I'm less experienced 
I'm on my phone so apologies for this being waffly and potentially incoherent 
Oh, and go for it! After a very slow and steady, on and off, process, we actually have a home that is functional, fairly clutter free, easy to manage and nice to live in. I avoided the talk of Minimalism for a while because I thought it was all white boxes and no TV, but turns out it's much simpler than that!