1. Spread things out a little so you are not stuck seeing the forest rather than the trees.
 
2. Start with items that you know what do with. Put them away immediately.
 
3. Pick items up one by one and force yourself to look at them.    

Once you have put away the items you know what to do with you may see categories emerging. If items don't have a home or don't fit in current location keep gathering them up in their 'like' groups.
 
After you have your categories of stuff sorted out you will be in a better position to gauge what else can get tossed, donated or recycled, and where the keepers should be kept.