Enjoy It
I would say first and foremost that you should carry with you one of those pocket size notebooks and a pen. Carry it with you everywhere you go. Scribble down feelings you get from your days. Ideas will often drop into focus from out of nowhere, jot them down or you will forget them.
Enjoy what you write about, it should be a fun thing, if it stops being fun, stop writing, take a break and do something else, you can always come back to it later.
Write about what you know and what you feel deep inside - that's where the emotion comes from. Unless of course you're writing science fiction or fantasy.
Read often. Experience gained from reading other writers work is an invaluable source of guidance on writing your own pieces.
Don't believe the hype. Sometimes folk will excitedly comment on what you write, enjoy it all, but take it with a pinch of salt and keep your feet on the ground.
Be prepared for writing stints that can go on for hours upon hours, and the turmoil you will feel when no one likes it. It happens. No problem when it does, learn from it and be patient. It will happen often.
Be honest with yourself about finished pieces of work. Be critical of it and correct even the tiniest of errors. Use a dictionary and a good thesaurus to keep your words and phrases crisp and correctly spelt.
Finally, don't over complicate your sentences (something I am guilty of on occasion), try and keep things flowing in an easy style that makes reading a cinch.
But, above all else, have fun.