Check locally for consignment stores.
With most, you agree to a specified price, with percentage discounts taken at certain points (10 days, 30 days, 45 days, 60 days, etc.). Each store has its own policy and they usually keep around 60% to 80% of the selling price. They are doing the work and paying the overhead. Some stores only pay in script, which must be redeemed at their store within a certain period. Try to avoid those, if possible. You won't be making anything--unless you really want something they're selling!
In all cases, clothing must be clean and in very good to excellent (nearly new) condition. Most of the consignment stores in my area sell only designer clothing for adults--they aren't interested in regular store brands, regardless of the condition.
You also might try Craig's List for your area. Try listing the clothing in lots--by size, type (flannel shirts, dress slacks, dresses, etc.) or something else that would make a fairly cohesive lot. Don't expect to get much for them--usually 10% to 20% of the original price, if you're lucky.
I sold a lot of my mother's clothing (mostly new) on eBay several years ago (about two years after she died), and did all of it in lots by size and coordinating colours. Didn't make much (typically sold a lot of 8 to 10 items for $20 to $25), but found a few people who wanted her specific sizes (14 and 16) and liked the colours/styles. Haven't been on eBay since 2006!
Good luck!