Let's start with the basics.
What is a comma?
I'm sure most of you know this already, but a comma is a pause in a sentence. It prevents confusion and is needed in your story, like it or not.
Examples:
1) As I climbed off my bike and ran towards the school I heard my best friend Lilly calling my name her voice hoarse.
2) As I climbed off my bike and ran towards the school, I heard my best friend Lilly calling my name, her voice hoarse.
Which one is better? If you say the first one, you are wrong. Very, very wrong. So wrong in fact that you should be ashamed of yourself. Seriously. You're better than that. *shakes head in disapprovment*
Now, why is the second sentence better?
If you re-read the first sentence, you will find yourself reading it like this: AsIclimbedoffmybikeandrantowardstheschoolIheardmybestfriendLillycallingmenamehervoicehoarse.
If you read the second sentence, you will notice yourself pausing at the commas and actually reading what is written instead of having things thrown in your face with no pauses whatsoever.
This is a great link for commas, and I suggest you bookmark it for future reference: http://www.grammarbook.com/punctuation/commas.asp
The above link will show you ALL the rules for commas. I, personally, don't have the time to list them all, so that link will explain everything. :) I hope you guys find it useful. If you do, let me know below!
Can I use a word twice in one sentence?
Yes, you can. But, I only mean words like a, the, and I. Why? Because they're general words and are very, very common, so it's okay if you use them twice in a sentence. But try not to use them more than that!
Now, for words like bag, hair, and love, do not use them more than once!
Example 1) As she put the change in her bag, she slung the bag over her shoulder and walked away.
Example 2) As she put the change in her bag, she walked away. Oh, how she loved her bag.
Which one do you think is better?
If you said Example 1, you are wrong.
If you said Example 2, you are also wrong.
You might be thinking, "Wait, what? Why is the second one wrong?"
Well, the second 'bag' is too close to the first 'bag.' Avoid putting the same word in a sentence close by. Use the word once in a sentence and move on. Then, two or three sentences later, throw the word in again.
Now, this is only a suggestion. You don't HAVE to do what I talked about in the above paragraph. It's not like you're breaking the law and the grammar police will arrest you for it. But I do suggest you avoid it as much as you can.
Can I use text talk in my writing?
Never, ever use text talk! I'm not joking. I will seriously smash my head against the wall for hours if you do. Not only is it annoying, but it's so unprofessional.
Does this sound professional to you?
"OMG, ILY BECKY!" I screamed, and she LOL'D.
"OMG, I'M SRY ASHLEY. I GTG. TTYL!" She ran out of the room.
Would you read a story like that? My thoughts exactly.
Can I write '2' instead of 'two'?
When writing, please do not write, for example, '2' instead of 'two.' Do not write with numbers (1, 2, 3), write the SPELLING of numbers (one, two, three). It looks way better, trust me.
How can I avoid run-on sentences?
READ OUT LOUD. If you have a sentence you aren't sure about, read it out loud. If you are out of breath by the end of the sentence, you need to chop it in two.
Example of a run-on sentence: As I stopped to catch my breath, I looked at the rays of sunshine above me that seemed to almost dance and it motivated me to keep going and never give up and I smiled as I began running once again and then I spotted my friend across the street.
Yikes! That's ONE sentence and it's three lines long. Now, how do you split that in two? Whenever you feel there is a pause, put a comma (like I mentioned above).
Here is the fixed run-on sentence: As I stopped to catch my breath, I looked at the rays of sunshine above me that almost seemed to dance, motivating me to keep going and never give up. I smiled as I began running once again, and as I rounded the corner I spotted my friend in the distance.
Although I added in a few words, you see how much better it is?
Tip: Avoid using 'and' a lot.
Example: I felt really sleepy and hungry and I saw my friend and I love Chinese food and I'm cute and I'm in love with a vampire and I'm failing all my subjects and...
Please do not do that. Do not use 'and' more than twice, and if you need to use it a third time, start another sentence.
Do I HAVE to capitalize words and add in periods?
Yes. I mean, are you THAT lazy that you can't take one second out of your time to press the 'Caps Lock' button?
When writing, always capitalize the words at the beginning of a sentence. Also, always capitalize the letter 'i' when it is used by itself.
Periods.
They are super important. They mark the ending of a sentence, and without one, your story would basically look like one giant mess. Or a run-on sentence that is fifty pages long.
It's pretty much common sense not to do that.