Hi smileyfacexo, from my past experience where I have undertaken the 'huge' task of tidying my then teenage daughter's room about once or twice a year, here is how I see the task-
1. Make a rough estimate of time of how long it will take. (I've had weeks)
2. Make a list of all the visible tasks on a big sheet in your kitchen - there will be invisible ones too and we'll get to that.
3. Divide the tasks into daily units of half hour or hour. No more no less.
4. Each day tick off the tasks - you will feel good as the ticks increase.
5. Arm yourself with disinfectant, air freshners, (bio degradable) plastic bags, cheap plastic containers - large and small, labels, so you or the person can find things later.
6. Be absolutely ruthless about throwing useless objects out into recycling or wherever.
7. Listen to 'sweet' music or radio documentaries, stories, debates. You're gonna get mad or tired, so you need distraction.
8. Begin with the simplest tasks and those you like. Keep the nasties to the end.
9. Don't worry about 'order', at first. Your mind will naturally start to categorize and sort things as the days and weeks go by.
10. Clean and re-clean where necessary.
10. Take a photo of the before and after.
11. Look out for the invisible items - soiled stuff, hidden stuff, the nasties - wear a mask and gloves if necessary. You won't know what you're breathing in or touching.
12. When you're finished, give yourself a treat.
13. Take one last look and check if there are some more things that can be dumped, recycled or re-used by someone else or indeed, sold.
I hope that suits. Cheers.