Board Thread:Off Topic/@comment-25396609-20160205040608/@comment-26397825-20160209124307

It's not so much an instant Mary Sue to have connections between your character and the main cast. It's when you character majorly effects the main cast in some way, is their best friend out of everyone, replaces them for some important thing, accomplishes canon plot points faster or better than the main character did in the original work, or just plain shows them up at everything that the character becomes a Mary Sue.

Minimise interactions before the start of any story and have them develop naturally over the course of said story and you avoid most of this as long as you don't overshadow them simply because 'it's your character'. If you're still unsure, there are a variety of Mary Sue tests available on the internet which will help you determine if your character falls into that category.