I've probably seen dozens, if not hundreds, of shampoo commercials and really they all promise the same things. They all guarantee smooth, shiny hair and the models they use make you think that you, too, will have long amazing hair cascading down your back if you use their product. Some companies even resort to using sex to sell shampoo; just look at the commercials for Herbal Essences products—women in the shower with soap lather coating their shoulders while they utter orgasmic wails. Seriously—that's ridiculous. Using a company's shampoo will not give you the subliminal promises the advertisements make, so then how do you pick a good shampoo if you can't trust the marketing?
Like most other hair care products, the use of shampoo narrows down to personal preference in the end. Apart from your own opinion on what works best for you, you should also consider your hair type and what you want your shampoo to achieve (apart from cleansing your hair). Like conditioner, shampoo can be found in many a variety all promising different results so you need to do some hygiene introspection and figure out what your hair needs are. Is your hair dry? Is your hair too oily? Is your hair colored? Do you have naturally curly hair? Do you have split ends? Do you blow dry your hair and need heat protection? All of these are some of the questions to consider when deciding on what kind of shampoo to insert in your everyday routine.
If you're having trouble figuring out your hair needs on your own, you can always talk to your hair stylist and see what they recommend. My best hair advice (I know—shocker) comes from my salon. They're usually really good about outlining the different options I have and letting me choose from there. If you get your hair colored I'd definitely buy color-protecting shampoo; it's way too frustrating to cough up the money for color that doesn't last.
Another thing to consider when selecting a shampoo is how often you wash your hair. If you wash it everyday you'll want a milder shampoo that won't damage your hair. If you shower every other day or so, feel free to go with a more intense shampoo. (You can go milder, but just make sure the shampoo is still cleaning your hair the way it should.)
One last thing to look at when purchasing a new shampoo is the ingredients it contains. Shampoos that contain proteins, milk, balsam, vitamins, moisturizers, oils, waxes, lemon, allantoin, silk, sunscreens, and polymers are all good bets for a good shampoo. (These ingredients also include some conditioning elements.)
Shampoo is a pretty easy thing to shop for and once you know what you want for your hair, not difficult to find the right product. Good luck in your shampoo quest!