When I started working, I used H&M to get what I thought were "office-appropriate" clothes. They were, but my office leaned a lot more casual than I'd anticipated.
While I wouldn't necessarily want to go teach/sub in yoga pants & a sweatshirt, I might think about upgrading a couple of tops, checking that my jeans didn't make my backside look awful, and getting a nice blazer or cardigan (assuming it gets cold where you live!) and maybe some lightweight scarves to punch up my look to a little more "grownup" but not overly formal look.
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Liz
DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle