Copy all very good images, original version, of appropriate time/place/subject into a folder. Don’t look too closely and make no judgments yet about which you will choose to enter. Cast a wide net. Start with more than you need.
Open images with a simple viewer. Zoom to 100%. Delete those that are out of focus. Cut down your numbers.
If you have time, post-process all those that remain. If little time, cut first. Compose carefully. Crop and size appropriately (to contest spec or to print size). Cut out the least good ones. Get help from a friend. Second person eliminates your biases. Read rules carefully (grasshopper).
Digital image contest: Pick the best and enter them.
Big budget: print all, then decide which to enter, mount them.