These are some very basic things for new writers. If you see somebody that could benefit from this, send them a link!
1. Use correct punctuation, spelling, and grammar everywhere, not just in your writing.
I see a lot of writers that text-talk in conversations, leave out punctuation, don't capitalize words, etc. Even if you're just shooting a message to a friend on Facebook remember those rules! Not only does this create good habits, but I find that it leads to better and more intelligent conversations
2. Learn those tricky rules like "laid/lay" and "effect/affect".
A lot of people slack off on these. Personally, I have to look up things like this all the time because I just don't remember. They're annoying, but learning the differences can help you out in your writing and in real life. Also, the difference between "good" and "well" is a must-know! I hear this used incorrectly every single day.
3. Paragraphs and when to use them.
Obviously your writing will be divided into paragraphs. Some people abuse this, some people don't use it nearly enough. If you're not sure when to use them, pick up a book and read just one chapter. Pay attention to how much information is put into a paragraph and ask yourself why the author chose to start a new one where they did. Also! Use a new paragraph every time a different person starts speaking. I thought everybody knew this, but I see it a lot. You cannot have two characters speaking in one paragraph. No. New person? Hit enter.
4. He said she said we said they said....
Make sure to include some action in your conversations. If two people are talking back and forth, what else are they doing? Drinking tea? Walking down a sidewalk? Check out this lesson to learn how to fluff up your conversations and make them more important to the story: [link]
5. Don't overestimate the internet.
I see a lot of writers get discouraged with the attention their work receives, especially on DA. Even I am a bit let down that my stories don't get much traffic. However, you have to keep in mind the nature of the internet. Pictures and art are easy- you click on them, look at them, and you're done. Think about a writing thumbnail on the website. The only thing the person can see is the title and the first sentence. If that doesn't grab their attention, they move on. Not every first sentence can really be an attention grabber. The best way to get your work seen is to add it to groups and ask people to read it. Also, check out fanfiction.net and fictionpress.com.
A lot of people don't put any research into their writing, which lowers the quality substantially. Imagine you were reading a story set in Feudal Japan and the characters were wearing jeans and driving cars. Obviously this is an extreme case, but you want to make your story believable! If you're going to write about a character who is a firefighter, do research on firefighters. Ask yourself, "If a real firefighter read this, would he find it believable or would he sit there going 'yeah right'?"
7. Proofread, for the love of monkeys.
Just trust me and do this: when you finish writing your chapter, get up and walk away from it. Do something else for at least thirty minutes. Now go back and read it to yourself nice and slow. I see so many mistakes that I know the authors would have picked up on if they'd reread their story. If you reread it right away, you'll probably miss a lot of these. You will probably still miss some mistakes. If you can, go back in a week and reread it again. Just because a piece is "finished" and up on the internet doesn't mean you can't go back and improve it for future readers.
8. Use dictionaries and thesauruses.
If you aren't sure of the meaning of a word, take a minute and look it up. It could save you from some embarrassing situations. Also, look up synonyms for simple words like "run" and "said" and "looked". Don't cram your story full of big giant words that you don't understand. Just try to get some variation.
9. Avoid painful cliches.
Don't describe eyes as "glittering orbs." Don't describe the way your character's hair flows in the wind and reflects the sunlight ten different times. Don't name your handsome hunk "Damien". I could go on for hours, but its best you check out some of the great resources on DA that are all about writing cliches.
10. Ask for constructive criticism and feedback.
Nothing irks me more than when somebody puts up a piece of writing and says "I know it sucks, don't try to tell me how to fix it." You cannot improve if you don't keep an open mind! Most critiquers will be gentle. Allow them to help you!
And the Golden Rule: Read books!
“If you don't have time to read, you don't have the time (or the tools) to write. Simple as that.” ― Stephen King