This helped us. Take 3 empty boxes: Label them: Toss, Donate, keep. Start with one category: Kitchen items: Set a timer for 15 minutes. Go through that area of stuff and fill the toss and donate box and try to keep the "Keep" box to a minimum. Once the the toss and donate boxes are filled OR if the timer goes off, seal the Toss and Donate boxes with tape and then Put the Keep items into the now decluttered and clean area.
IF the area isn't clean, either continue cleaning if you wish and try to fill 2 more Toss and Donate boxes or take the keep box and move it to the area where you will need it. Continue working in 15 minute stretches. It should help you from getting overwhelmed. When going through your things, try to fill 2 -3 donate and toss boxes to every 1 keep box. Do not put the keep box away until you have cleaned that area. Get rid of the Toss/Donate boxes the day that you fill them, otherwise, the things may creep back into your areas.
If you have a friend that you trust, bring them in to your fold, if they wish to help. Have them be your honest assessor of things needed vs things to toss.
If you get stuck on keeping or donating/tossing, ask yourself, will I use this in 90 days? Am i putting an emotional attachment on this item and feeling guilty to get rid of it because of "X,Y, Z"?. If you get stuck on things because they were a "gift", remember, people give you gifts becasue they think you might like/need them. It doesn't mean you have to keep them forever, a gift is yours to do with what you wish, if there are strings attached to that gift, then it wasn't a gift at all.
For important docs, try doing electronic storage in a cloud or external hard drive. Then shred docs that you don't need to keep because you have the nitty gritty e-filed away.
If you need storage area, think UP, vertical storage is your friend in small spaces.
Good luck, decluttering and reducing your life "stuff" can be very freeing.