Rules of thirds with the horizon. not in the middle.
Unless you have to pay, you have nothing to lose by submitting to a competition, if it doesn't come anywhere, look at those that do. You have to be in it to win it. The worst that will happen is they wont like it. If it doesn't win, just move forward, there are likely to be loads of entries, so it wont mean your not any good, just not good enough on this occasion.