Here's a plan, which happens to be what I do. Please feel free to adapt it to suit your needs.
Invest in a set of standard boxes that will stack. The box I chose has a 40cm x 30cm footprint, in thick cardboard. It's crucial that all the boxes have the same size footprint so they stack. You may need 50 or more of these. Clear some space in the least used room of the house and stack the boxes against the wall. You'll also need labels for the boxes.
Whenever you come across something in the house that you think you probably do not need to keep, box it and label the box. If you subsequently need the item, you can find it by checking the labels, and retrieve it. But you'll find that most of the stuff you've boxed is not needed and can indeed be given away (or sold).
After a while, you'll have a stack of stuff you wish to dispose of. You can then decide which charity shop to take it to - I choose the ones that demonstrate the loudest appreciation for the items I take there. Every bag of stuff taken to the charity shop is a victory. Keep your boxes. (I used to use ebay but I find it increasingly time consuming, and it becomes a chore in itself, which is counterproductive. I've also used Freecycle and Gumtree, but found that no-show customers were a drain on resources and counter-productive.)
Disposal of the items in your stack frees up all your boxes and then the process can begin again.
As I say, please adapt this plan to suit your needs, but this is working well for me. The advantage of doing it this way is that I'm dealing with just one item at a time on a daily basis, and it has become integrated with every day life at home.
The final part of the plan is this:
Do not put anything into the loft from now on. Instead empty your loft and dispose of everything there. You're doing this on the grounds that the stuff in there is not used sufficiently often to warrant space in the house. Lofts are not meant for storage. Just to prove this, once the loft is empty, top up the loft insulation. This will be a financial investment since it will save on heating bills.