A look back at what once was popular and it's now a fashion faux-pas. (Faux-pas is French, literally meaning "false step", aka: a fashion blunder). Try to avoid the following:
Tie-dye
Try to get shirts with 1-3 colors.
Fanny packs
Fanny packs add volume around your tummy-- something we want to avoid. Use a purse to carry your necessities around.
Overalls

Little girls look super cute in these, but I would probably skip them as an adult. Also, that second color blue makes the jeans look like one flat color-- we want a tiny bit of variety in a jean color-- refer to Wardrobe Staples to see good jean examples.
Velour jogging suits

Activewear should be looser fitting to allow for movement and that doesn't look like velvet. The above outfit will quickly show sweat in a lot of places, embarrassing! Also, activewear should be worn only if you are exercising.
Something like this is just fine. I like to wear white t-shirts (they are cooler temperature wise).
Big-patterned shirts/ Shirts with too many colors
See how our eyes go right past the face of the models and straight to the shirts? These are busy and often make the person look bigger. We want people looking at you, not a busy shirt. It should compliment your beautiful face and draw eyes there. Try something like this:
See how our eyes are drawn towards her face?
Tucked-in shirts
Try not to tuck in shirts. (You will see pant models tucking in their shirt, but that's just to sell the pants). Longer shirts will generally elongate your torso and make you look taller and thinner. Something like this:
Big back pocket jeans

These make your tush flat and wide. Take a look below for a good example:
Pockets should be smaller and just on your tushy. See how it makes things shapely here?
Tapered pants
They taper down to your ankle and end there. Pants should go past the ankle-- almost skimming the floor. Those will flatter you much more.
Sandals and socks
If it's cold, wear shoes.
Whiskered jeans

Whiskers belong on cats, not your pants. ;)
Light jeans and black shoes or vice-versa

Also, white socks with black pants or vice-versa should be avoided. See how it cuts her outfit into sections? We want outfits to flow.
White washed jeans
Ugg boots
Try to get more neutral colored boots that are more sophisticated. If you like boots, go for something like these: