You've probably gathered that I'm a fan of writing competitions especially free to enter ones. You may also be aware that I'm very keen on woman's magazine fiction (my other blog contains all the guidelines you need to submit, plus tips, news and advice on writing for this market). You'd think then that I'd be in favour of writing competitions run by woman's magazines, offering prizes and publication. In theory I am, but I do urge you to read all the terms and conditions very carefully – including those you have to go online to discover.
Many such competitions require you to give up all rights (search copyright on the womagwriter blog if you're unsure what that is or why it might be a bad idea). Now you might be thinking that's fine, if you get published and win a prize then you're prepared to give up the rights in that story – but in some cases this condition applies to all entries. Just by submitting it you will have given the publishers the right to do whatever they like with that story, and deprived yourself of the right to ever use it again yourself.
What are the rights to your story worth to you? I suggest they are at least as valuable as the fee you'd earn if the story was published in another magazine. Assume it's one of the lower payers – £40 – and ask yourself if the competition really justifies that as an entry fee. If not, perhaps you'd be better off submitting it directly to another publication, or entering a competition which is genuinely free.