Prior to this year, I had spent a number of years ignoring how I looked, wearing the same pair of jeans or yoga pants and boring tees. Now that I am having fun with clothes, I can be like a kid in a candy store when I go shopping. It's hard not to want to buy anything that looks good on me! But I have also identified "wardrobe holes", and I am trying to keep those in mind. Especially because I am realizing that $20-$30 impulse buys quickly add up to the amount I COULD use to invest in the bigger-ticket items I really need. So, for example, yesterday I tried on a sweater that looked adorable, and was only $30. But I know I've been looking for a great pair of boots, which will get a lot of wear. So I admitted that I didn't want/need the sweater enough to justify spending $30 that could go towards boots.
I find this forum, fashion blogs, and Pinterest have helped me prioritize my fashion wish list. I scan through my "My Style" board (where I pin outfits or items I love) and look for repetition. For example, I posted enough outfits that included a denim button-down shirt to realize it made sense for me to buy one. Same with booties. I see lots of outfits I'd wear them with, so I know they're a good investment.