As a writer, the best advice I could give is to READ.
Sounds strange right?
Not to say that learning grammar and spelling aren't important or building your characters up, but reading is a critical aspect of writing.
And I'm not just talking about reading/editing your own stuff either.
I've read a lot of tips on writing and everyone says the same thing, it's important to read.
Here are the reasons why
1- Reading gives your mind a rest from actually writing your story, but allows to you continue to be receptive to inspiration. Struggling with writers block? Take a break and read a book. It usually is enough to get those creative juices flowing again.
2- As you read, you pick up on grammar and vocabulary that you can later use in your own story.
(I've noticed with my own writing that I do this all the time.)
3- As you read, you learn about more character development. If you feel like you keep repeating the same mannerisms in a character, reading may give you an idea of how to spice things up a bit.
4- You will begin to mimic the flow of the stories you enjoy the most, as in the flow of your words in your story. For example, you will have less awkward stops between sentences and learn to portray dialogue in a natural way.
5- Reading many genres will expand your creativeness. It is important to keep a constant feed of inspiration coming through, or else you will never grow. You can only recreate yourself so many times before there's nothing left to pull from.
6- Reading is like taking a vacation, even if you can't afford one. It's a stress reliever and stress is one of the reasons writers get the horrible disease known as writers block!