Having trouble letting go of things you know you don't really need?
1. Pretend you're moving. Ask yourself: is this item worth packing up, carrying out (or paying a mover to pack up and carry out) and unpacking?
2. Cultivate a healthy attitude. You're not just getting rid of stuff -- you're recycling, or giving it to someone who needs it more than you.
3. Once you've filled bags with trash and donations get them out of your space as soon as possible, preferably the same day. The visual improvement will inspire you.