Nobody sits down and writes a bestseller on the first try. To my knowledge, it's impossible to find a person, much less an experienced writer, who puts forth a grammatically correct, perfectly balanced, and shiny piece of literature at first chance. The genre doesn't matter---poem, book, short story, research paper, that dull statistical analysis you're writing for work---more likely than not, they'll all fail to impress when written the first time.
And that's okay.
I don't mean to be pessimistic; I only intend to stress the importance of rereading, rewriting, and editing. As a full-time Editor myself, I can't emphasize it enough.
(As Stephen King once said, “To write is human, to edit is divine.”)
Your first draft is your chance to get all of those ideas flying around in your head like anxious birds on paper. Release them. It doesn't matter where they fly at the moment; just let them out so they can stretch their wings. Type (or write) your thoughts and see where they take you. Right now, your grammatical skills or the amount of passivity in your sentences doesn't matter. Just write.
Now that you're sufficiently pleased with releasing those birds and they've calmed down a bit, it's time to get them in order and read what you've written. My process usually looks something like this:
You'll find that, not only will rereading/editing your work in multiple drafts make you a better writer, your piece often goes in an unexpected, and better, direction. To view an example, let's look at this poem I created for the purpose of this exercise.
First Draft (Free writing):
It definitely needs work. Let's move on to how it changed when steps 1 and 2 were applied.
Summary of revisions made: Capitalization where necessary, em dashes inserted when breaks between lines weren't full sentences, “within” the current removed since it was strange
Now that this is moderately presentable, it's time to really look at it.
Summary of revisions: “It's hard to know sometimes” section revised and moved to end of poem for emotional impact; "It's hard to know sometimes" changed to "I often wonder"; “Floating from river to ocean” added to tie in river theme; “then, too” added for clarification; “under the weight” removed since currents don't really have weight (do they??)
And the finished product...
I'm not touting this as the best poem ever written, but even this short piece shows editing works wonders. This blog post itself will undergo the same editing process before it's posted.
Returning to the original point: your first draft will likely need some work. But spend the time looking it over, revising it, and giving it a little love---and you may create something magical.
Writer, editor, and storyteller living in the Twin Cities.