I always thought the best advice for winning a competition was 'shoot for the competition', don't just dig through your archives and try to find something that fits.
Don't get me wrong there's some good stuff in here but I reckon, along the lines of the above point, that it cheapens a competition when submission notes say:
"If you'd like to enter the same image into more than one category, please tick all that apply."
http://poty2008.dcmag.co.uk/
I presume this comp is centered around novice submissions in the true sense of the word, although some of the images belie that notion. Anyone entering competitions at the moment?