As a freelancer and believer in the written word I have many hats - some I wear for money and some I wear for the simple love of the hat. Two of these hats involve poetry competitions - one I sift for (for money), the other I print all the poems for and send them to the judge (for love). I have been donning these hats for several years and am frustrated by how many people shoot themselves in the foot when entering poetry competitions.
I thought it might be helpful to list some dos and don'ts. I am not an expert. Like you I enter many competitions and don't get anywhere. I have won a couple of competitions and both times I thought the poems unlikely to win. This list is by no means exhaustive.
1) Difficult and emotive content
It is painful reading poetry competition entries - not because the entries are bad (although inevitably some are) but because people are baring their souls and telling you their deepest (and darkest) secrets. There are many poems that move me with their content but will never make the shortlist because they are not doing enough as a poem, or are too oblique, or are simply prose broken into lines to look like a poem. This is sad for a reader - some of those poems have important things to say. Some feel like a cathartic exercise for the writer but are not offering much to reader. A poem about trauma (or loss) needs to offer something to the reader too. A poem is not a misery memoir - though it can touch on the same subjects. I actually find poems more powerful if they are less explicit in their content (I like this in films too) - something alluded to but not explicitly spelt out - a good example of this is the poem 'The Bicycle' by Katrina Naomi from her book What the Crocodile Taught Me.
Another way into difficult subject matter is to use metaphor.
2) Size isn't everything
Short poems are good, they can be very powerful - but it's unlikely that a haiku will win a major poetry competition - they just don't stand a chance against those poems that have more space to make their point. Save them for short poem competitions - Magma has a short poem category in its annual competition. Of course, there is every chance that I may be proved wrong one day.
Similarly there are poems that feel way too long. Some of these go off at odd tangents (this may work in a prose poem but works less well in a conventional one). Some say the same thing over and over in a variety of ways. Some poems feel like they need the ending and beginnings lopped off - the introduction and the explanation. A good poem feels tight and not baggy. Frisk your poems thoroughly for superfluous weight - you should be doing this anyway, but it's even more important for a competition poem.
tip: One technique I use is to take longer poem and make it shorter to fit the competition guidelines. Sometimes it can't be done, but often it can - and usually the poem is better for it.
3) Write like you live in the twenty-first century
It's as simple as that. I see many poems that read as if they were penned in the 1800's - loaded with words like 'hast', 'thou' and 'whence'. The only time this is acceptable is if you are writing a pastiche - but it's dubious even then. If you are writing like that because all the poetry you read looks like that, then you need to start reading modern poetry. If you don't know where to start get in contact with me and I will send you a reading list.
tip: Don't expect to love all modern poetry - you need to find the poets that speak to you. You wouldn't expect to go into a library and like the first novel you pick up. Poetry is the same.
Syntax is important too. Beginning poets often think that poetry is some kind of special code and this leads to poems that sometimes don't make grammatical sense - sentences without clauses, sentences that are broken up in odd ways. A poem should be written the way we speak. Try reading your poem out loud and you will soon hear if the sentence structures are odd or unnatural.
Rhyming is fine - personally I like a bit of rhyme - but it has to be good. If you are rhyming because you think all poetry has to rhyme then please go back and read number three above. Good rhyme can be amazing - it doesn't whack you round the head shouting I am a rhyming poem - in fact sometimes you might not even notice the rhyme at first. Other times the rhymes want themselves to be noticed. Similar effects can be had from half rhymes, slant rhymes and repetition. A word should never feel like it's in the poem simply for the rhyme scheme - better to ditch the rhyme scheme or put the poem away for a while and hope the right word comes to you.
5) Angst and anger
In the course of sifting/printing and teaching I see many poems that express deep felt sorrow, grief, angst or anger. While these poems may be cathartic to write - they offer little to the reader. If a poem's message is 'I am angry - really angry' - the reader is left with the question, why? If you need to write an angry poem tell us why you are angry or at least hint at it.
If you are despairing and feel like the world hates you - please give us some clues as to why you feel like that (and see a counsellor). These kind of poems are frustrating to me as I feel the raw emotion of them but they also leave me a little cold - they don't let me into the world of the poem/writer. I think that's the difference between therapeutic writing and poetry for general consumption - my morning pages are not for anyone else's eyes. I can moan and rage in them and I don't have to explain myself. If I want to put those emotions into a poem I have to offer the reader a way into them too - they have to care about the narrator or feel like there is some kind of universal truth that they can relate to, an 'oh yes that bothers me in that way too'.
Grief poems can be really difficult too. Sometimes we need a bit of distance from the loss. Sometimes we need a lot of distance. It has been more than ten years since my brother died and I still find it hard to write about. Some of the most successful poems relating to loss of a loved one are about the small things rather than directly about the loss itself. Penelope Shuttle's 'Peter's Shoes' is a great example of this. We all understand what that 'year' means - yet she hasn't felt the need to spell it out. The use of 'you' and 'your' in the poem is clever to - it addresses the dead person but allows the reader to bring their own meaning to the poem (their own lost or dead) in a way that using the specific name throughout wouldn't.
6) Subject matter
Pretty much anything goes in terms of subject matter these days but there are some things to be wary of (and, yes, I have definitely seen all of these):
a middle class white person writing of the black experience
poems about murdering young women that read like a script for CSI
explicit sex for the sake of it
ekphrastic poems that describe the art work/painting that they are based on, but don't do much more than that
poems based on historic events that just describe the event and don't offer us anything new (be careful with this type of poem of overloading it with facts from all your research too)
anecdotes about something that happened and simply that - sometimes these are just prose chopped up to look like a poem
Anything goes in term of form really - although as I said earlier a Haiku is unlikely to win a major competition. Poems in strict form can and do win as do poems in free verse. The trick is to do it well and for the form to fit the subject matter. Also check whether your poem is actually a poem and not just a piece of prose chopped up - could it be a prose poem, a bit of life writing or a short story?
8) The Title
You would be amazed looking through a mailbag for a competition or a journal at how many poems have the same title. I must have read a hundred poems in the last year called 'Lockdown' for instance. One line titles like'Lockdown', 'Snow' or 'Rain' are best avoided. I would also avoid titles that are a pun - especially if it's a serious poem. You also don't want a title that gives away the whole poem or a title that is a line of the poem (this takes the power away from the line in the poem). Titles are notoriously difficult. If you are having problems ask your workshopping group or a writer friend. Sometimes when I have been really stuck a friend or a tutor has immediately suggested a title that brings the poem alive.
9) The ending
I talked earlier about poems that feel like they should end sooner. Beware of over-blown or summing-up endings. Trust your reader - you really shouldn't need to spell it all out for us. I have noticed that some great poems go a bit weird towards the end - sometimes a really good poem will suddenly go all poetic, start using archaic words, or hit us round the head with a bit of moral guidance. Similarly some writers feel the end to end on a pun, a joke, or a punchline. Trust the poem to do the work. Endings are hard but there is shortcut to the perfect ending. Workshop your poem if you are having trouble, pay for a critique, or put the poem away for a while so you can come back to it with fresh eyes.