Start with one room at a time, and choose one corner of it.
Get three bags or boxes - one to "keep", one to "bin" and one to "freecycle/charity shop".
Sort everything in the corner into the boxes, and move across the room, decluttering everything in this way.
When you have cleared everything out of the room, vacuum, dust, polish etc.
Put back the contents of your "keep" boxes - or leave them in the box if they should go in another room.
Get rid of the "bin" and "freecycle/charity shop" stuff.
When you've done this to the whole house, write yourself a cleaning routine and stick to it - for example you could thoroughly clean one room each day, and keep up with dishes/laundry every day as well.
I've just done this and it is helping quite a bit