A good story needs a basic storyline with alot of description.

For a wild pokemon story let's take the simple statment:

I walk into the grass to catch a pokemon.

This is basicly what you are building off of in most cases, unless you decide to get creative and not just catch pokemon in grass..... Which i would enjoy to read. But hey this is just a sample!

Now lets beef that statment up with the W's...... and an H. You should all know theses:
Who What When Where Why How

So for who: You but use your username. Mines: Pandra
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For what: the statment says what your doing already. You can add on. But i'm just saying this for the example
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For when: any time really. Examples are:
1873 (I don't know why, so don't ask)

my first day of being a pokemon trainer

after i stopped in(a place) - This is an good example. You don't always need to know when but what comes before.

and times of day like night, afternoon, etc.
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Where: Self explanatory really. Where are you? In a field outside of a city. Just try to make in interesting.
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Why: Probably to catch a pokemon......... (or maybe you heard a scary noise:0)
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How: Now your story is about HOW you catch your pokemon. How doesn't mean "I threw a pokeball". It's the fight, the description of the pokeball throwing, the intense waiting, and the like.
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Descrition: This is just adding in things to make it more exciting. No it's not a "W" or an "H" but its very important.

So now let's beef this baby one step at a time.

Before: I walk into grass to catch a pokemon.
First we will do description.
After: I walk into the tall, waist-high, grass to catch my very own pokemon.

Now lets add where and when, just because they are smaller things.
After: It was a bright sunny day, and I had just left Vatmaden City. I had entered a large field with tall, waist-high, grass. I walked in to see if i could find any pokemon.