Despite the gruesome title of this post, the question is valid. How do you decide what you want from a girl? How do you decide if she is one night stand material, dating material, marriage material, or jail bait?
Simple: you make your decision based on how she makes you feel.
Guys try so hard not to react to women, to be alpha, to be like a mountain. No one wants to sleep with a mountain. React to women! When you see an attractive girl, your wanting her is a reaction. When you see an unattractive girl, your not wanting her is also a reaction.
But reacting to girls not only based on their looks but on the way you interact with them, you'll get the girls that make you feel good and turn you on. You'll also avoid the girls that make you feel bad and turn you off.
If you feel awkward or angry around her all the time, then chances are she's not the one. If you feel confident and sexy around her, go get her, tiger.
Alpha is owning your reactions, not avoiding them. What you choose to do with your reactions, your emotions, is what separates the men from the boys.
Choosing to show interest "too soon" only means you chose to show interest before you were actually interested, not that you showed interest before she was ready to accept your interest. Her acceptance of it has nothing to do with your desire before you reveal said desire. However, her reaction to your wanting her does have a lot to do with your following reaction. If she treats you like a dog or a punk after you make it known you want her, avoid her. Attraction is a two-way street.
In short, showing interest is like walking onto a car lot. It doesn't mean you're ready to buy the car you want at any price. It only means you're looking, trying to find out more. If the salesman doesn't present good terms, you can still walk away. It's the same with girls. Showing interest is not the same as signing a check.
Show interest freely. React freely. Commit sparingly. Commit only if it feels right. Commit only if she makes you feel good about who you are.