So, there are a lot of tutorials for writing; tutorials for character's names, personalities, storylines, and everything else under the sun. Don't get me wrong, some of those tutorials are pure gold. But, and keep in mind I'm no avid tutorial-reader and I haven't read all of them, I have yet to find one about editing. And it's about as important as the actual writing, because what's the writing if you can't read it? So, here I am, making one. If you've already read this far into the introduction, do me and you a favour, and read the rest of it, you might find some of it useful and I won't just be talking in a void. Please?
View of an Editor
So! You have your piece you're going to edit, haven't you? What's the first step, before you start editing? You have to get in the right frame of mind. Repeat after me! My writing is not perfect. Yeah, that's right. It's not. It won't be even after editing it. Writing can be wonderful, amazing, beautiful, emotional, and brilliant, yes, but never perfect. That's why writers must always be open to suggestions and criticisms. Because no matter how long you write for, no matter how much you edit and revise it, no matter whatever you do, it. Will. Not. Be. Perfect.
Got that? Right, now on to the next step!
Character reference sheets
I know, I know, Character reference sheets are only for dumb role-playing games with lots and lots of information on them. Right? Wrong. The character reference sheets are essential for writers to. You don't want your character to drop a vowel there or change an eye colour here half way through the story. I'm not saying write tons and tons of useless information about them. Heck, unless it's super important to have the height and weight and whatnot, all you really need is the name, age, the appearance, the gender and the species. You can even take those last two out if you want to, because they're easy to remember. Here's an example:
Blonde, blue eyes
Put them on an piece of paper or something or other, and keep it close when you're writing or editing. Add any names of special groups, for instance if you're writing fantasy and the magic group has some really long name with one too many A's.
Wait for it
If you edit something you've just written you've still got the scene and picture still fresh in your mind, so you can't read it like your reader will. A week at least. A month is better. A year is brilliant. Yeah, you don't have to wait a year, a week will do. Now, print your piece out-- if it's really long, take at five pages--and grab a pen and get ready.
Now it's time for the REAL editing!
Typos and extra spaces (Suggested by Tiamate.)
Ok, so it may seem obvious but it's really important. If half of what you write is unreadable garbage then how is your reader going to get involved in the story? Always capitalise your "I"s unless there are stuttering or it's in a word, and never use text speak in a professional piece, unless in a rare occasion if it's a character's phone. I don't care if you were writing it quickly or you were tired or whatever, if you don't have the time to write it properly, why should we take time to read it? Also quite common is extra spaces and incorrect puncuation. I for one get extremely annoyed when I see 3+ ellipses (dot-dot-dots "...") and when more than one exclamation point/mark. If you have Microsoft Word, it picks up quite a lot of them, but not all of them so you still have to edit.
Repetition (Also suggested by Tiamate)
The first impulse is to use a character's name over and over again, and most new writers always use "The blonde" or "the raven head" or "The tall man". After a while, these phrases become stale and annoying. It's ok to use the character's name once every sentance, or once in a line if you're using short sentances. Also repition of, for instance, if Bob found a dress, he wouldn't contantly refer to it as "The dress", he would refer to it as "it" or some way of describing it. You need to find a happy medium with repetition.
Take out unnecessary description
It's ok to take out things. Words, sentences, paragraphs, pages, even chapters. Even Characters if they're slowing the story down or are weighing the plot down in some way (If you're going to kill them off, do it for a reason. Like the villain wants to taunt the main character, or if there is crazy evil ghost people floating around, and one of them sucks out their soul...) And since you're character isn't perfect, just like the writing, it's ok to do so. People do it all the time.
Let's think about it, a reader begins reading your work and is suddenly lost in a maze of complicated words or is wading through adverbial swamps or trying to find the needle of action in the haystack of unnecessary description. I'm not saying no description--god no-- Just know where to use it. For instance, say your character Bob is running through a spooky shadowy forest, being chased by a scary vampire who wants to suck his blood, he's not going to suddenly pause the action and start describing a interesting mushroom cluster at the base of a tree. Every time you describe something, the action slows or stops. This can be used, for instance if your character, say it's bob again, is in hospital for a week, you don't want to summarise it all. He's going to describe the room a lot more than he would have done the forest. But not everything, because you have to leave some of the unimportant detail to the reader's imagination, so they feel more involved with the story.
Information dump trucks are a bad idea
Ok, so you've taken out all other unnecessary words. Good for you. Take a moment to just sit back and congratulate yourself on this achievement. Done? Good. Now, onto the information dump. The description isn't the only things that slow down the stories and make them duller than dull. There's another hidden mistake just waiting to be made. It's the infamous information dump.
Especially fantasy, but all types of non-fiction, you're taking your reader to another place. If you weren't your story would be boring, a waste of time, because writing is meant to take you to another world, or another place or time in this one.
It's really easy to just go ahead and list all of the differences, start to finish, between this one and that one. Resist it. Dumping information is like dumping description on them. They're lost in your complex words and ideas. They can't make sense of it. They loose interest and stop reading.
Instead, put them on a drip feed of information about the new world. Leak it into them. Leave out uninteresting or unimportant bits. They don't have to know everything.
Don't have any bad characters
No, by 'bad' I don't mean 'evil' or 'villainous', I mean 'badly made'. That means little to no Emos and no Mary Sues. If you have a world full of moping and dark and misunderstood people whose entire family have been killed by evil demons and wolves and whatnot, and are now self-pitying 'misunderstood' emos, then I for one would get annoyed by everyone, and there would be practically no speaking at all. Mary Sues are perfect goody-little-two-shoes who have never thought a bad thought in their lives. These are just two examples of a universe of bad and annoying characters. Just get someone else to tell you if they hate them.
Edit other people's work
Not only is editing other people's work a good karma booster, it's also helpful, letting you hone your editing skills so you improve yourself and other's work. If you don't have time to help other people with their writing, you can't expect them to help you with yours.