There are different ways you can tackle the decluttering depending on what would work for you.
If your house is really cluttered, maybe just the first day, walk around the whole house and you'll probably be able to fill one carrier easily and maybe more from just what you can see.
Whilst going round, maybe decide which rooms are a priority and start to make a list.
Personally I would break it down into specific areas so that it doesn't feel too overwhelming eg bedside table, individual shelves or drawers. These you may be able to do in 20-30 minutes each and tick them off.
There are no rules with this - if you do say a bedroom area, when you make your coffee, do just one drawer in the kitchen. It really doesn't need to be done in order.
Don't take all of your clothes out of the wardrobes at once! This creates a big mess and totally overwhelming - just look through the rails and shelves and remove stuff.
When you first start to declutter, there's plenty of low hanging fruit - stuff that you can get rid of easily. That creates a bit more space and easier to see what is left. Then the next time you look at that space, you'll notice that there are a few other bits that can go and so on.
I have recently decluttered wardrobe of work clothes for example. The first day I got rid of 2 jackets. A week later, I had another look and another 2 went.
Do not try to do it perfectly the first time as it's hard and demoralising. I have found that if you get rid of some stuff the space makes it easier to see other stuff that can go.
Also you need to decide where you are going to put stuff for a charity shop run. It depends on the size/layout of your house. If you can walk to a charity shop easily like I can, maybe make that part of your new routine as the exercise is good. But don't make it a misery by trying to carry too much.
Or stick stuff straight into your boot in bags if u need to use a car.
Remember that the perfect is the enemy of the good - don't aim for perfection the first time round.
Good luck.