You should first consider donating furniture to Habitat for Humanity's local Restore. Sometimes furniture can be donated at designated locations. Be sure to give them a call in advance to verify their business hours and any criteria they have. You should also verify your municipal building. It's possible that they have a list of authorized donation centers. You should also check to see if there are donation pick-up options in (this link) your area. These providers will visit your home to collect the furniture.
It can be rewarding and satisfying to give your old furniture away to people in need. If you follow the advice here and give away any furniture, you can be assured that it will be used well.