"Have nothing in your house that you do not know to be useful or believe to be beautiful."
In keeping with the decluttering spirit, I'm going to keep this post short and simple. I think the above rule is the best you can follow when considering what you keep versus donate/sell/trash. I love love love this post from another blog that gives a list of 15 decluttering tips. If 15 is too many or the post is too long for you, allow me to sum up my favorite rules:
1. Remember the rule stated in the quote above. If you don't love it or need it, get RID OF IT.
2. Don't bring it into the house in the first place. If you must, follow this rule: 1 in, 2 out.
3. Clothing rule: If you haven't worn it in 6 months, donate it.
4. If you don't want to get rid of something because you were planning to sell it online or at a garage sale, give yourself a realistic deadline (i.e. 30 days, not 30 years) by which you must complete the task.
5. Hoarding is selfish. Your value is not in your stuff. In fact, your value goes up when you share stuff.
6. Gift everything. Give books away immediately after read, and donate old items when you buy new items.