I've got one answer. Just write the way you speak. You can't be more authentic than that. Your readers will get to know you better, because you are being your true self. You will enjoy it more, because you aren't feeling the stress of not being yourself. And you know what, I bet it's more interesting.
If you'd like more encouragement and a few more hints, click to read "7 Tips for an Authentic and Productie Writing Process".
ps don't you love this snail photo? I sure do-