Before I retired from the rat-race I was first in the West Sussex poetry competition (1992), first in the "short Fiction" (Univ of Plymouth) competition (2006), and placed in competitions run by "Varsity", "Cambridge Writers", "Kent and Sussex Poetry Society", and "Staple". I've more or less given up entering competitions nowadays - my poetry's more suited to magazines, and my better stories are too literary, I suspect.
I make exceptions for some competitions that are free to enter, have book-publication as the prize, have a theme that I've already written a piece for, or publish an anthology.
I belong to a writers group (Cambridge Writers) that offers free entry to their competitions for members. I don't think I've ever won their story competition. Often I don't even get commended. This time I managed second again - worth £70. I think I'll try harder next year.
My story collection "By All Means" (ISBN 978-0-9570984-9-7), published by Nine Arches Press, is on sale from 
My poetry pamphlet "Moving Parts" (ISBN 978-1-905939-59-6) is out now, on sale at the 
