Advice/Help Character development

[Mad-Moony]

I've made a lot of characters over the years as well as roleplayed with many different people. I was wondering if anyone had any advice or imput on how to make a character interesting, yet not cliché or overpowered/Mary Sue. I've found people have tried to make their characters cool and unique, but it just turns out like everyone else's or it's just plain childish...

Plus it's hard to take them seriously when their character is frolicking with their magical rainbow hair talking to their magical wolf soulmate that they were bonded to as a child...

Can anyone relate to this? Or at least have some advice on how to make a character not boring and bland yet not unbearably overpowered or cliché?

Thanks! : )