Only you (the indvidual) can answer that question!
Each of us selects our own friends, lovers, and spouse. You first of all have to (know yourself) very well in order to know what you want and need in a mate. Once you (know) what you're looking for it makes life a lot easier. The goal is always to find someone that (naturally agrees) with you on the major things in life and shares your same values. It takes some time being with a person to determine this. Having chemistry/attraction is also very important.
Last but not least: In order for her/him to be "the one" (they) must also (see you) as being "the one". The underlying definition of "soul mates" are people that have (mutual feelings) for one another and want the same things for their relationship/marriage. I remind people of this whenever I hear someone complain about their mate not wanting to get married. If you want to marry them and they don't want to marry you it's clear they (aren't) your "soul mate"!