My little tip is to accept and pass on hand-me-downs. I saved every piece of clothing from my first son. Five years later I had my second one and here I am, using all the old clothes. I am now saving baby's clothes that don't fit him anymore to give out to a friend who is expecting.
Whenever I go to yard sales where they have children's clothes and are doing "bag" sales ($1 to fill the bag), I buy up most of the kids clothes that are in good shape. I take them home and sort through them to see if there is anything that will fit my granddaughter. If not, I take the rest to a Kid-to-Kid location and trade them in for store credit. Then I can take my granddaughter shopping there for the clothes she needs. I did that the other day. I spent $4 and got $40 in store credit to spend!
My teenage daughter loves shopping at Plato's Closet. It is a teen resale shop that only carries name brand clothes like Hollister, Abercrombie and Aeropostle. They are located in many states. They are a bit more expensive than a regular resale shop or garage sales, but it is full of clothes all teens would love to wear. My daughter has bought $80 jeans for $12. Let someone else pay full price! Another great thing is they will buy name brand stuff on the spot from you which means cash in your pocket. We checked out Plato's Closet web site. It looks good.