One Toy in...One Toy Out.

With all the new toys coming to invade your house (from you, Grandparents, gift exchanges at school etc...) can your house handle them? Do you have the extra room for them to have a place to go? Will you be trying to figure out where to put all the new ones?
Try the "One toy in...One toy out" rule. For each new toy that comes into your house, find one toy that can be donated (or thrown away if its broken) to go out.
This can be done with or without the kids. You know your children. If they are ones who are going to pitch a fit and say they they can't possibly get rid of ANY of their things...then it is better to do it while they are not home. Don't pick out their favorites that they still play with. Find those ones that are underneath a pile that they haven't seen in months (or years) and get rid of those. Chances are they will never miss them. My children never complained or missed a thing that I got rid of over the years. HONEST!!
If you have children who have a heart for helping other children, then it may be good to involve them in the process. (Although it is probably the kids who have the difficulty giving up their things who really should be learning that other kids can really use the toys more than they can.) They will realize they are helping other children and will enjoy it. The triplets are good about this. I usually go through without them, but when they realize what I am giving away they talk about how much the other kids will enjoy using it.
Don't continue to pile on more toys just because YOU have an attachment to them. Kids can only use and play with so many things. Less is so much more in this area.