singing advice please?

ok so i am 13 and im not the best singer,but im not the worst either,
if you've heard of open mic uk then yeah if not is like a singing
competition,i want to enter it-its this august and i dont know if
there's any places left but i need some advice on how to get a better
voice. i have singing lessons in school but i would like privet ones,
if anyone knows anyone in cardiff who does singing lessons tell me.
thanks