Write the ideas down. If they are going to be stories, try and tell the stories you would like to read. Finish the things you start to write. Do it a lot and you will be a writer. The only way to do it is to do it.
I’m just kidding. There are much easier ways of doing it. For example: On the top of a distant mountain there grows a tree with silver leaves. Once every year, at dawn on April 30th, this tree blossoms, with five flowers, and over the next hour each blossom becomes a berry, first a green berry, then black, then golden.
At the moment the five berries become golden, five white crows, who have been waiting on the mountain, and which you will have mistaken for snow, will swoop down on the tree, greedily stripping it of all its berries, and will fly off, laughing.
You must catch, with your bare hands, the smallest of the crows, and you must force it to give up the berry (the crows do not swallow the berries. They carry them far across the ocean, to an enchanter’s garden, to drop, one by one, into the mouth of his daughter, who will wake from her enchanted sleep only when a thousand such berries have been fed to her). When you have obtained the golden berry, you must place it under your tongue, and return directly to your home.
For the next week, you must speak to no-one, not even your loved ones or a highway patrol officer stopping you for speeding. Say nothing. Do not sleep. Let the berry sit beneath your tongue.
At midnight on the seventh day you must go to the highest place in your town (it is common to climb on roofs for this step) and, with the berry safely beneath your tongue, recite the whole of Fox in Socks. Do not let the berry slip from your tongue. Do not miss out any of the poem, or skip any of the bits of the Muddle Puddle Tweetle Poodle Beetle Noodle Bottle Paddle Battle.
Then, and only then, can you swallow the berry. You must return home as quickly as you can, for you have only half an hour at most before you fall into a deep sleep.
When you wake in the morning, you will be able to get your thoughts and ideas down onto the paper, and you will be a writer.
Great advice from Neil Gaiman — how to write!