While I don't have experience with high-end consignment shops (the kind that requires you to set up an appointment to bring in your goods), I have frequently taken my items at places like Buffalo Exchange, Wasteland, Beacon's Closet, Crossroads Trading Co. and many others.
In my experience, these types of consignment shops only give you about 35% of what they sell the item for. In other words, if they buy your leather jacket and decide to price it at $30, you'll receive $10.50, which is 35% of $30. Some shops may offer you more (about 50% of what they price the item for) if you decide to forgo the cash and take store credit instead.
If you don't have any experience selling at consignment shops, my advice is to only bring your gently worn, name brand items.
Consignment shops are not to be confused with thrift stores; buyers are extremely picky. They also purchase clothing based on the season, so plan accordingly.
If you have a giant bag of your old college shirts and mom jeans, don't bother with consignment shops. Instead, drop them to your local Goodwill and get a tax receipt.