You could sit all day and watch extreme tidying videos on youtube. Whilst they can give you some good tips, the best thing is to just go for it.
If you have piles of clean and dirty laundry, gather them up into 2 piles. Whilst the dirty is washing, sort and fold the clean and put it away. Gather all dirty dishes and wash them up and put away. If you have kids with toys strewn around, get some tubs/boxes and put all the toys in. If the kids are old enough, get them to sort them out. If not, you can leave them in the boxes to sort out when you have time.
Gather paperwork into a pile and sort through.
Just work methodically. It is easier if you work with like items (laundry, toys, paperwork etc).
As you go, get large bags/boxes to sort things for the trash and for donating to charity (and selling if you are that way inclined). At the end of each day, or every couple of days, get rid of the things you no longer want. Once you have the rooms tidy, you can begin working on the cupboards and sort through those.
It is a freeing feeling when you get rid of all the things which are no good.
Good luck - who knows, you might find things you had forgotten!