I agree with a pp, don't hold out for making lots of money. The Royal Doulton lady that cost a load of money and was so carefully chosen is now worth £5 in a charity shop. The whole process goes so much faster if you focus on letting things go.
Unless of course your family heirlooms are actually valuable.
We packed up clothes first. Divided them into things that might sell and rags. There were some emotional things, like hats dmil wore to our wedding, dh found packing up his dad's suits hard. But it had to be done.
Then we did the kitchen. There's a big charity shop near us that sells even the most random of mugs and plates, they have shelves that are 3 items for £1 or something like that.
Ornaments and vases and the like also went to charity shops once people had chosen what they liked.
That was manageable to do, but the volume of stuff was unbelievable. I can't even count how many trips it took us.
Furniture either to the dump, charity shop or local facebook groups.
Paperwork, photos and diaries we boxed up and took home with the intention of sorting through eventually. We've had mixed success with that so far.
It's a horrible job and took a huge amount of time. But I'm glad we did it. It felt like the last thing we could do for them,.
But don't feel guilty if you use a clearance firm. Not everyone has the time to do it themselves.