The first piece of writing advice I believe has merit, is to write often and write properly.
While it sounds redundant, it is far too easy to procrastinate. Days pass and suddenly 6 months have rushed down the river and you are still standing on the river bank. Alone, with that good idea. Now, you feel self conscious and unconfident. It is daunting to restart, so don’t stop.
I say write properly, because this is my own personal weakness. It is so important to use good grammar and punctuation. Johnathan Swift is quoted as saying, ‘Proper words in proper places makes the true definition of style.’
So you are ready rock at using commas, and write regularly as you drink a cup of tea?
Well, second on my list would be assessing the market. Determine where and who accepts freelance or unsolicited work. Study them until you are comfortable with their style, and then start searching for topics. Make a list of ideas, then discard the first three. If you thought of them first... so has someone else.
Now for individual publication analysis. Really assess their publications under a microscope. If you are looking to publish something with a magazine make sure your opening sentence has the exact same number of words as every other article in their issues.
Saying that if you have an awesome piece that is already written search out a place that already publishes things in the style you have already used.