I have been on a months-long mission to de-clutter our house by de-owning our stuff. I have read a lot about how beneficial it is for kids to grow up in a clean, clutter-free, organized house. Here are a few of the benefits: (1) their brains are able to focus on more important things than having to process the visual (therefore cerebral) distraction of clutter everywhere; (2) they pick up good habits like cleaning up quickly and keeping things organized when they grow up in a house like that; (3) their parents are able to focus more time on them rather than having to run around looking for stuff and constantly battling junk everywhere; (4) parents also benefit from the calming effects of a clean house, which shows in the way they parent; (5) kids learn to really use and enjoy the toys they own rather than jumping from thing to thing to thing in a room or house filled with a million toys. The list goes on (and those of you who know my kids are probably laughing because my kid are little hellions a lot of the time, but imagine how cray they would be in a chaotic house!) ;)
Another benefit is that when it comes time to move (and we are all bound to move at least a time or two more in our lives), the process will be SO. MUCH. EASIER. I learned this lesson the hard way. We moved a few years ago, and we were so overwhelmed with STUFF that I had to sort through, pack up and move that I wound up straining muscles in my feet that resulted in debilitating pain for many months afterward (like, I couldn't stand up through an entire pump-it-up party or soccer game) and lingering pain that still flares up from time to time. So I decided that when we moved, we would start living like we could be ready to move any time (in terms of our stuff and the way we keep our house.) If my husband was transferred to another city or state for his job, we could be ready to roll in a matter of days instead of the many weeks it took previously. I try to embrace minimalism in terms of keeping only what we truly use on a regular (or at least a seasonal) basis. Clothes we outgrow or don't wear for over six months are automatically out of there. Same rule for toys. We have a "one in, one out" rule for both clothes and toys now (and gadgets, etc.) For example, I really wanted an ice cream maker, so I had to part with the chocolate fountain that I love (but seriously have used like three times EVER). :)
I also try really hard to keep up with things like making sure to quickly paint over scuffs or stains on the walls, repairing shutters that are broken in our indoor soccer games, replacing ripped screens on windows, etc. I remember the hell that getting our house ready to show on the market was, and I never want to repeat that! I hope and expect that we will be in this house for at least the next ten years, but not only would be be showing/moving ready if the time came, but we are able to enjoy our house a lot more while we are still in it!!
I have finally pared down our seasonal decorations, mementos, sports equipment, etc. to just what remains in our garage. I also thought I would be more likely to keep up with it if I tried to think of our garage like any other room in our house by painting it and adding a little decor. It actually is the most important room in our house, because we park in there and enter our house through the garage, so I want to make sure it sets the right tone when we enter at the end of a long day! :)
In short, start small, start big, just start SOMEWHERE. Have a big old pile out on your curb each month for bulk trash and donate the stuff that is still usable! Take pictures of anything you feel sentimental about. (I mean, keep the things you feel REALLY sentimental about (i.e. your kid's first pair of ballet shoes, but be prepared to be really ruthless. You will be SO glad to be FREE of the clutter. It really does change the way you live.)