At some point in everyone's life they come to the realization that they have too much stuff. First you need to decide whether you want to donate or sell. There are several options to consider:
1. Donate to a charity. If you give to a nonprofit charity get a receipt for a tax write off next year. Some thrift shops accept donations at their store but others won't. The Salvation Army near me accepts drop offs behind the store while our Goodwill doesn't. There are also thrift shops run to fund shelters and soup kitchens. Give them a call before driving out. If you have large items that are too heavy for you or won't fit in your car, some places come to your home. The charities that come to my home are Purple Heart and ACRC (American Cancer Research Center). If you want to donate something large to a non-chain charity just give them a call. Perhaps an employee can swing by your home with their pickup one day. That's how I unloaded my old couch.
2. Donate directly to a needy family or cause. Perhaps you know a family on a tight budget that could benefit from your contribution of outgrown clothes for their kids. Ask them if they could use something that's still good, but about to be tossed because you've outgrown it. Your church might know of someone in need. Make some calls. I ended up donating a perfectly good, but old and now too small, refrigerator to the local fire department to use in their lunch room.
3. Sell it on Craigslist.com. This is free to you. Choose the city in their listing that's closest to you and get started. It's your option on how interested parties contact you - phone or email or confidential via craigslist channels. I use the confidential choice. I highly recommend you put up at least two photos of different angles and maybe any details that make your items look appealing. Give good descriptions and measurements. Mention whether several strong people are needed to pick the item up and whether they might need a pickup truck or SUV. See what everyone else is doing for similar items on Craigslist and be better than your competition! I sold an IKEA loft bed for $100 recently. I got 4 emails in the 1st day. My advantage - I had photos when the competition had none, and my price was a little cheaper.
4. Sell it on Ebay. This is not free. There is a charge to list your items and they take a commission off the final sale price. Because of these two charges, the system doesn't work very well with small ticket items. If you can, bundle small items together as a lot. For example, instead of selling my daughter's outgrown clothing piece by piece, I put all the fall/winter clothes of the same size together as a 30 pc lot and scored $101. Do a search for similar items to see what opening bids and final selling prices are. Sometimes it's emotionally difficult to start something at a low price but that's what sparks the excitement in bidders. The clothing auction I mentioned started at $10 (yes, I prayed it wouldn't sell that low and was very nervous at first). What's great about Ebay is that it's like a yard sale that isn't ruined by bad weather and the whole world is your market. I have sold to the USA and Canada. My friend sold a lot of clothing to a lady in Spain. Regarding shipping - that's paid by the buyer in addition to the final purchase price. You just type in the weight (don't forget the box) when you set up the auction. Ebay is linked to the post office's chart of zones and shipping speeds and the shipping price automatically comes up to you and the bidder when they check out your listing. By the way, you will need a Paypal account to buy or sell on Ebay.
5. Post a flyer with tear-off tags listing your phone number, the item and cost. There's the bulletin board at the grocery store, gym, lunchroom or bulletin board at work. Ask friends to post at their work, too. I sold my 82 Datsun 210 by handing out homemade flyers to my coworkers. Ends up the cousin of one of my coworkers needed a car! Also try the bulletin boards at the local colleges. I sold a table to the mother of a soon-to-be college-bound girl who needed dorm furniture on the cheap. That one was posted at my gym.
Good luck to you!