I don't know how old your kids are...
Start with organizing your house. Make sure there is a "place" for everything, so when you want them to "clean up" they know what that actually means because everything has a place where it is supposed to be. For example, I can't stand it when I'm tripping over shoes-- but it's not fair to a child to just say to stop leaving their shoes all over the floor if you don't have a specific place where their shoes are supposed to be kept (in their own closet? in a special place by the front door? pick whatever makes sense for your family and make it CLEAR to everyone)
Once it's clear where everything goes, set a rule that no one can do anything fun (computer time, family time, going out to play, whatever-- again-- I don't know how old your kids are) until the house is picked up. (This can be a Saturday morning thing to get ready for the weekend, or a daily thing after school) Give them specific tasks that are age appropriate. We had a big clean up yesterday because my older 2 wanted to have sleepovers. My 4 year old wasn't just told to go "clean his room"-- he was shown a particularly messy corner of the living room and asked to put those toys where they belong, with his 11 year old sister nearby assisting him if he needed help. She (the 11 year old) was also responsible for picking up the rest of the living room, which does NOT mean to find your own stuff and leave everything else. She knows what belongs to who, so she needed to put away her own stuff, put away general stuff (like a bag of chips that needed to go back in the pantry) and distribute her siblings' stuff to their rooms where they were then responsible for putting it away. My 12 year old was responsible for cleaning the dining room table (the family dumping ground!) and getting all stray shoes (not just his own) by the front door where we have a spot for them.
Once the house is clean, it's much easier to keep up with it daily by pointing out when they plop something where it's not supposed to be or play with something and not put it away when they're done. Depending on the age of your kids (and mood you're in-haha!) you can say that anything left laying around will disappear-- and that could mean being put up high where they can't have it for a few days, or put in a box in the garage for a week, or whatever seems appropriate for your family. If they act like they don't care if/when things disappear, threaten yard sale and follow through!! If part of your problem really is too much clutter, have a yard sale and encourage your kids to give things up by letting them keep the money (all or part) of things that are theirs