I know how you feel. My house was pretty cluttered (i go through phases of extreme bargain hunting and shopping) ive got better in the last year.
I think before u declutter you need to stop the flow of crap coming in. For me carboots and charity shops are weaknesses. I dont take my card and no more cash on school run so not tempted to pop into shops. School paperwork read/recycled as soon as it comes in, same with junk mail/letters.
Sort bathroom/kitchen and use all supplies. Dont buy more until all the random shampoos/tins have been used up. Meal plan and buy as required.
In bedrooms throw out all the holey/mismatched or scruffy clothes. I had a sack of odd socks after a year or more the other isnt just going to turn up.... sell on or charity shop clothes you/children wont wear eg dds had at least 8 party dresses each they didnt need that many so passed on a few.
Dvds/cds go through and if u dont watch or want anymore scan them on music magpie/ziffit. They even collect i think.
In terms of cleaning i do the basics everyday - 1 wash load hung up and put away, clean kitchen, wash up, sweep downstairs, wipe around bathroom, put away things after using (shoes on rack, remotes away etc girls encouraged to do same). Then on weekends hoover upstairs, deep clean bathroom/kitchen, dust/polish, hoover sofa.