The biggest mistake that people make is to go shopping only when they need a specific item. This puts incredible pressure on to find exactly what you need when the stores just might not be stocking it. When I was working in retail, it was not uncommon to have clients come into the store on a Friday looking for a dress to wear to a wedding the next day. Often they were visiting from out of town and expected that Chicago stores would have a better selection than their hometown. But by shopping with a time constraint, their selection was limited by several factors. The first was that if we didn't have the size in stock, there was no longer the option to order it from another store. Another was that we might not be having any sales or promotions which meant that the perfect dress was now out of their price range. Since they were trying to buy something before the stores closed (which on Michigan Avenue was between 8 and 9pm), they didn't have time to comparison shop. Maybe they would have found the perfect piece at the perfect price at a store two blocks away, but because they were desperate to just buy anything, they never made it past the first store they went into. Compounding this problem was that they were trying to choose a dress that worked with the shoes and accessories that had brought along so they could avoid spending even more money on coordinating pieces.
Of course, you should still use your judgment when buying things that catch your eye. You may fall in love with five different sequin evening gowns, but unless your social calendar includes at least five black tie events a year, you should probably hold off on purchasing them all. When deciding whether or not to buy something, ask yourself whether you can foresee yourself wearing it in the next six months and if you think you will still like it in six months. If you answer yes to both of those questions (and it is not a duplicate of something you already own), then you should go for it. These questions are especially important to ask when the item is incredibly inexpensive. It is easy to be blinded by the low price and not think about how useful the piece will be in the long run.
When you are shopping, don't be afraid to try on new things. Take an adventurous friend with you or enlist the help of the sales associates and have them pick out pieces for you. Commit to trying on everything they bring you, even if you are sure that you won't like it. If you don't pre-judge the items, you will open yourself up to discovering new styles that look incredible on you! Some of it will probably look not so great on you, but that's also okay. That's the reason that we try on clothes before we buy them.
If trying on clothes in a store is discouraging for you, try online shopping. I personally hate bra shopping, so I recently ordered several styles from Nordstrom. They offer free shipping and returns so there wasn't any pressure for me to keep the pieces if I hated them. I could try them on in the privacy of my home and see how they looked with various tops. If you often get pieces home from a store and find you don't love them as much as you did in the fitting room, then this is your solution. Zappos also offers free shipping both ways and except during big sales, so does Boden.
For an in-store experience that is more leisurely, do your shopping during slow times, such as weekday mornings. You won't have to fight the other shoppers to find your size and you'll also benefit from having the full attention of the sales staff. If you have a favorite store, call them up a day or two before you want to go shopping and see if they can set up an appointment for you with a sales associate. Let them know what pieces you are looking for and your size so they can set aside some of their favorites for you to try on when you get there. If you build rapport with a sales associate, pass on your contact info along with a few notes about styles you are interested in. Ask if they can let you know when items arrive that they think you might like. They'll be thrilled to know they you will be a repeat customer!