Op, I feel your pain. I rarely wear anything other than jeans and a Tshirt but as a future teacher, I've had to amp up my wardrobe. I'm far from an expert and I shop at Goodwill, thrift stores, Ross etc so I'm not one to spend a huge amount of money on clothes. I can offer a couple of tips from my own experiences.
I have had success in the last week at Target. On Clearance, I found a pair of real slacks, a sleeveless navy print wrap top and a nice sweater for $25. I often buy printed tops that I can pair with camis or cardigans and a variety of pants. For example, I just bought a navy blue long sleeved print shirt with green, purple, blue pink and beige leaves. I can wear it with black slacks, gray slacks, khakis, dress it down with jeans or add a jacket and nicer jewelry to dress it up.
I rarely buy solid colored dresses simply because I find prints o be much more versatile and easier to fit to the occasion.
Another store I love is Beall's. The clothes are not designer by they have a good selection of plus sized clothing at reasonable prices. They also sell costume jewelry so it's easier to see what a particular item would look like dressed up or down.
The key to clothes shopping, I have found, is to always try it on if you think it may fit. Some of the best fitting clothes I have were ones that I was convinced to try on by someone else. I can feal with a print im not in love with if it makes me look skinnier!
Also remember that baggy clothes can make you look bigger. Finally, I can't emphasize the difference a good pair of control top undies can make in balancing out your shape. I am an education major and I honestly look a size slimmer on bottom when I wear my Spanx. I can also wear a size Smaller in slacks when I have it all "sucked in".
I wish you great look shopping! It sounds like you've received some great advice and that you're well on your way!