A lot of people I work with ask how to decide if something should be kept or gotten rid of. There are a couple methods of figuring that out, some more painless than others.
There's the "Friends and Enemies" game. When looking at a pile of items, keep the items that are "friends," and get rid of the "enemies." Simple, really.
There's also the well-used three question process. When looking at a particular item, ask yourself these three questions:
1) Do I need this item, in the most literal sense?
2) Do I use this item? Be honest.
3) Do I love this item?
And still, there's the numbers game. Decide ahead of time how many of a particular item is reasonable to own. Then, count how many you really have, and whittle down the pile until you meet your goal number.
However, all of these processes are getting you at the same answer. Which of these items makes your life better? Which items are your "friends?" Which do you love? What is actually useful and makes life easier?
When looking around, are there items that remind you of times you'd rather forget? People that are no longer an integral part of your life? Jobs and places from which you've moved?
Pick out the items that make your life better. Not the items that remind you of things past or goals you never fulfilled. After all, who doesn't want an easier life filled with friends and love?