Construct a simple sentence and identify the subject (or main noun). For example, you can make the short sentence "Birds scattered" more descriptive by using an adjective to modify, or describe, the noun "birds." Make a list of the most important qualities of this noun and choose the adjective that conveys the most interesting or surprising aspect of the noun, or that gives the reader information about the noun that will affect his understanding the person, place, or thing being described. The birds in your sentence may be frightened or afraid if you are writing a horror story, so your sentence would read, "The frightened birds scattered."
Avoid redundancies when picking an adjective. It's important to choose one that will give information the reader will not already have. Your audience will be aware that water is wet, so using that adjective to describe a pool of water does not add anything to the sentence. Instead, you could describe the water as being cool, warm, bubbling, shallow or icy, and write a sentence like, "The bubbling water poured from the mountain spring."
Show, don't tell. This standard piece of advice given to writers means that you should use descriptive words that create a vivid image in the readers' mind. For example, instead of telling your audience that it was a hot day, show them by saying that, "the woman hopped down the scorching pavement in her bare feet, and her skin turned red as she stood under the intense sun."
Familiarize yourself with the various types of adjectives. Most people think of adjectives as things they can easily visualize. But remember that an adjective is anything that modifies a noun, including articles (a, an, the), numbers, demonstratives (this, that, these, those) and comparatives (more, less, very, etc.). In most sentences, you will use an article naturally. In the sentence "The bike was expensive" you already have one adjective -- the article the. You can add a demonstrative (that) and a comparative (more) adjective by writing "The bike was more expensive than that one."
Be specific and accurate. Think about whether the adjective logically goes with the noun it is modifying. If you can't easily imagine a table being "scintillating," but a table can be "polished." Strive for accuracy every time, even if you have to use a more common word instead of a more sophisticated, but less accurate, word.
Separate adjectives with a comma if you use more than one adjective of the same class to describe the same noun. are writing more than one adjective in the same class together. The classes of adjectives are opinion, size, age, shape, color, origin, material and purpose. In the sentence "The big red balls bounced," you do not need a comma between big and red because big is in the size class and brown is in the the color class. In the sentence "The thin, flat package arrived" you do need a comma between the adjectives thin and flat because both describe the shape of the package. The opinion class refers to an objective way a person feels about a noun (such as funny, ugly or brilliant).