This question contains its own answer, and the answer depends on the path before you.
Traditionally, you do not approach a Mason. They approach you — having observed your character, your conduct, and your compatibility with Masonic values — to recommend you to the lodge. This was the way of it for generations: the Mason sought the man, not the other way around.
Alternatively, you may join by making a direct application to the lodge. This modern avenue exists precisely because good men sometimes walk alone, without a Masonic connection to vouch for them. The application process — detailed above — exists to ensure that no worthy man is turned away simply because he has not yet met a Brother.
Whichever path you walk, the destination is the same: the scrutiny of the lodge, the examination of your character, and the unanimous ballot that decides your admission. The method of approach matters less than the sincerity of your intent.
In 1779, when Wolfgang Amadeus Mozart sought admission to the lodge Zur Wohltätigkeit in Vienna, he was already known to the Brothers through his music and his reputation. But he still had to ask. He still had to be examined. He still had to be voted upon. The approach was merely the first step; the work of proving himself worthy was his alone.
The Bottom Line
Whether you are invited by a mentor, recommended by a Brother, or moved to apply directly, the threshold of Freemasonry demands the same thing from every man: sincerity, discretion, and a genuine desire for self-improvement. The path may vary, but the obligation does not. Knock, and it shall be opened unto you — but only after the lodge has looked through the wicket and found you ready.