Well. I have four boys, so keeping them in cute clothes that aren't a mess at some point during the day is a challenge in and of itself!
But, I do have a few shopping tips - mostly because my husband thinks he is Dave Ramsey, so in order to dodge an argument, this is what I do:
Planning ahead for the season - Summer months - t-shirts, shorts, and swim trunks. Winter months - sweats and socks. tons of socks! we constantly loose socks. So I will already have my eye on these kinds of items when shopping, whether in department stores, yard sales, or discount stores. It helps to know what your kids will be needing for the season. We dress in "Sunday best" for church, so I've always got things on hand for weddings or other special events. But if you know you are going on vacation or you have family photos planned then it is a good idea to have some basic pieces that will get good use and that you can add accessories to.
Which leads me to the next tip - accessories are not just for little girls! A hat, colorful sneaks, or a cute belt can go a long way!
Shopping out of season - GAP, Children's Place, and Old Navy have really great end-of-season sales, some at 50% off. I buy plastic tubs and fill them up if I find things that I know my boys will wear in the future.
Stocking up on basics - discount stores like Target and sometimes Wal-Mart have really great solid color tees for under $5.00. Pair them with plaid shorts and flip flops in the summer or sweats and tennys in the winter.
Consignment shopping - sometimes I find great items, sometimes I don't. One time I bought a brand new pair of Nike Tennis shoes for $9.00 that last my son almost a year, so it is always worth my time to at least take a look. I can usually find like-new sweaters at a price I am willing to pay vs. brand new and ridiculous. Hint: If you hit a consignment shop before the next season really begins, you will find better deals.
Since I have all boys I can usually "hand down" as the boys grow out of it. Because of this, I can justify spending more money on certain items that I will know will last. So I put all my kids clothes that haven't been ripped or stained or really worn into tubs and organize by size. Eventually one of them will be in SOMETHING that is in that tub. And this is not for everybody because it is absolute hell trying to go through 5 different tubs looking for 4 different sizes every. single. season. But, it does save money.
And finally, know what your kid will wear. Or, what you will make your kid wear. No use in spending money on something you know he/she will only wear once. This goes along with planning.