There are a few things you can do to make your clothes look really good without spending a ton. I definitely recommend places like Nordstrom rack to get clothes but taking care of them properly makes a huge difference. Making sure there are no stains, rips, fuzz balls, lint, and that the clothes fit properly is 90% of it. I highly recommend finding a food tailor and taking a couple pieces there. There are things a tailor can do that aren’t very expensive and will completely change the overall appearance of the clothes. Things like hemming your pants so they’re not too long, or putting a couple darts in a blazer, or even putting a little snap fastener between buttons on a button up shirt if you get gaps between buttons. I highly recommend the book How to Get Dressed . It has so many tips and tricks for making your clothes look amazing, whatever they cost.
I learned a lot from the old 'Dress for Success' books for women. The one my mom had was published in the '80s, but the information is still good.
There was a new one published in 2014.
Information about what's class vs. trendy, how to decide how many shoes you need for a work wardrobe (if you can't afford many, buy one quality pair in a neutral color, other than black, neutral & navy in cheaper shoes), different jewelry for work & socializing, etc.
I'd start with that one.
This is the best seller in that category on Amazon right now, and looks interesting:
I found 'What NOT to Wear' useless, but the books by Stacy London (with or without Clinton Kelly) are pretty good.
Knowing your colors is important too. If you have the money, I'd pay to get that done - it's called a Seasonal Color Analysis. My mom & I had it done when I was a teen. Every time I fell in love with a shirt or dress that wasn't on my color chart, I would always gets comments such as 'you look tired', 'are you feeling ok?' or even, 'what's wrong?'
If you don't have the money, try this online one:
http://www.thechicfashionista.com/seasonal-color-analysis-2.html
A third way to figure it out is look at your wardrobe. Which outfits garner you the most compliments? If you group them together, you'll find they usually are a certain range of colors/tones. Which outfits get you comments like the ones I listed above? They will have commonalities as well.
If you don't remember, just get a good mirror and some sunlight. Hold some of the fabric up just below your face. Hide the buttons, trim, sequins or anything else that distracts.
Some of them will be obvious. I remember at the class there was a demo. The teacher put a pretty yellow fabric up against her face. It drastically accentuated the bags under her eyes, and added a good 10 years to her appearance. After finding a few of those, you'll start to notice which ones do that to you.
Forget fashion shows - I used to try to learn from those, until I had a friend explain the difference. Fashion shows are about artistic concepts and showing off the designer's talents. The models are too thin and extremely tall - so nothing will look like it's on a real person anyway.
Fashion magazines have some of those same flaws. For me, the most realistic images are from clothing catalogs. If you are big (like me) or short (also, like me) look at the specialty catalogs. Even though the models are still too perfect, airbrushed, etc. they are the closest to real humans.
There are some subreddits just for fashion, and you can browse their FAQs and even submit pics of you in a certain outfit for feedback.
Good luck! And keep in mind, just because you learn the rules doesn't mean you have to follow them. Sometimes I want to look hideous/sickly - want to get a Friday off work, but not suspected of playing hooky? Wear a terribly colored outfit, no make-up and call in sick the next day. No one will question it (unless you put idiotic stuff on facebook).
Want to go out drinking with the girls and not be pestered by men? Everyone pick ugly colors. They may be defeated by beer goggles eventually, but then you can break out the fake moles from the Halloween store.
I love a sunshiney, buttery yellow. It's my favorite color. Sadly, it makes me look like I have jaundice. I just use it in my house instead - accent pillows, a brightly colored throw, even one wall in a room.
So, hope this helps you.