NB. These tips are for poetry writing, though some may be useful for fiction writing too.
1. Once your piece is written go through it and take out any words that don't need to be there. If a piece works without the word then it's likely it doesn't belong. You can always put it back again! It should become obvious which are the 'culling words' the better you get at it. Words that repeat a lot like 'and', 'the' come into this category. I love culling!
2. Is it concise? Does it ramble trying to do too much or do you actually need more to express what you want?
3. What about line structure and pattern. I find that once I have edited so far by hand I need to type it up. This gives me a feel for the poem on the page - how it looks. It is often at this stage that I might change the shape by splitting into stanzas, trying different combinations and line breaks. Again you can change it back if it doesn't work.
4. How does your poem sound? Read it aloud see where it flows, where it stutters. What is it's rhythm? Where are the rhymes? Are you using end rhymes? If so, do they feel forced or cliched? Internal rhymes work well (my favourite). How about metre? Is it working or is trying to break out into something else? Sometimes as I write I find that a poem tells me where it wants to go, whether it wants to have end line rhymes or go 'freestyle', or follow a form like a sonnet or villanelle. I've learnt to go with it. However, there is no harm in trying several ways (or forms) to write a poem and see which one works best.
5. Perspectives - whose point of view is your poem putting across? Try changing third person to first person or even second person. Does it sound better or worse?
6. Titles are important but sometimes the most difficult to choose. Do you give it all away by the title or use some subtle word/s for your masterpiece. Does it reflect the poem and relate to content? I remember once in a class everyone loved my poem but some didn't like the title (which I was stuck on). Someone suggested that I just left it untitled but the best suggestion was using the first few words of the first sentence as the title and that's what I went with.
7. The most important part of editing is to put your poem away for a few days or a week, maybe longer because when you next look at it all those niggly things stand out and the second edit has begun. Continue doing this until you are completely satisfied that there is nothing else you can do to improve it. Sometimes a poem just won't come right. Put it away and leave it for a long time. Come back to it now and then and have another go. Maybe it needs a complete re-write. Maybe the form is wrong. Whatever you do don't throw it away. Maybe you can use some good lines or phrases somewhere else.
8. Is editing every over? Ha! I think not! I have seen poems I've had published and thought....'Mmmm, that's not the best word I could have used.' But writing is a journey and over the years our writing changes with experience. There is also the tendency to over-edit which is also frustrating because you get to the point where nothing is left of the original.
These are just the editing tips I've learnt, read and tried over the years. Writing good poetry means reading it too. Read different poets. What makes their poetry sing for you? Take their poems apart and analyse them. One of the best books I have come across on understanding poetry is 52 Ways of Looking at a Poem by Ruth Padel. This was a real eye-opener for me in understanding how poetry works. Greatly recommended.