Mistake #1: No specific list
When shopping for items that you need/want, make a list and be as specific as possible. Ex: black blazer that hits at hip, rounded shoulders, 3/4 length sleeve.
Lesson: Don't be afraid to get super picky--the more specific and discerning you are upfront, the less likely you are to waste money.
Mistake #2: Compromising on fit, quality, or style
Here's the thing: style does not need to be expensive. I shop at Target, Old Navy, and H&M. But the problem begins when you purchase something that you "NEED" right now, or you find a piece that's almost what you want and buy that instead of paying a little more for the exact I-can't-wait-to-wear-this-forever piece because the former was cheaper. Sometimes this is okay, but if the clothing doesn't fit well or you're not dying to wear it, you probably won't.
Lesson: It really depends on the quality of the item. A lot of my closet staples come from Target, others I have to get at Nordstrom. Sometimes it's worth the money spent upfront to get multiple uses out of an item.
Mistake #3: Doesn't fit your lifestyle
I wish I could wear high heels and a pencil skirt everyday, but that's not where I am in my life right now. High heels + toddler = sprained ankle. Therefore, it wouldn't make sense for me to purchase two skirts for the "someday" when I will get to wear them, even if they're ONLY $20 each. If I only pull them out of my closet twice a year, that's $40 I've wasted. I've bought items that still had the tags attached when I gave them out. There is nothing sadder than that.
Lesson: Buy items that fit the season of life you're in now.
Mistake #4: Not knowing your style
I love the boho look, but I'm not really one to wear hats, skirts, or boots all the time. I know that because I've spent time on Pinterest looking at pictures of outfits that I think are cute vs. outfits I know I'd actually wear. It's fine to love a piece of clothing you see in a magazine or online, but rather than going out and trying to recreate that exact look, try to take a step back and see the themes or general commonalities in the items you've collected.
Lesson: Rather than recreating an entire outfit that doesn't match your style, try to find themes within items that draw your attention.