She Doesn't Return Your Phone Calls
A very simple way to tell if a woman is not interested is if she never returns your phone calls. If you find yourself listening to her voicemail box more often than her real voice, it's time to move on. Also, be concerned if she does pick up her phone, but immediately says she's busy and that she'll call you back later.
She Talks About Other Men
Notice if the woman you like constantly talks about other men. If she always talks about how great she thinks a certain other man is, it is likely that she is more interested in him than you.
She Never Asks You About Your Life
A woman who isn't interested in you won't ask you many questions about yourself. She may ask you simple questions, such as how your weekend was, but she won't ask for details. Someone who is into you would want to know intimate details about your life, such as where your family is from or where you see yourself in five years.
She Starts Arguments
It is perfectly normal for men and women to have their share of arguments, but it is time to be concerned if the arguments are started for the most silly reasons. For example, if she makes a big deal about you eating the last piece of cherry pie, she is trying to pick a fight. This could be a sign that she is unhappy with the relationship and wants to end it.