It depends on what you are looking for and the type of girls make your d!ck hard and stimulate your mind.
Aside from looks:
She must have some social skills and can hold a convo and we can have that psychological, mental orgasms from time to time, this is rare with girls but there are girls who have this quality.
She initiate contact more often and invite me for some interesting venues and things, she must be creative and surprising, again this is rare
You must establish your dominance and call her out when she is being stupid you call her stupid, when bitchy you call her bitchy and see her reaction if its a submissive one then cool, if she is bitchy about it you know this girl is not that much , and remember call her out but don't argue
Trust your gut like others says.
Qualify her and sh!t test her very often and always keep her on her toes, Game is really simple, you reverse their game on them and see the magic happening.
If she doesn't work out or think gym and staying healthy is not important I won't meet her ass again but that's just me and I just plate and have an abundance mentality, i don't know about you guys if you have reached this level or not yet.
There are other stuff but you get the idea. you simply look for high SMV in girls and reverse their game on them.