I've noticed that people generally good at practicing reciprocity -- the act of giving back the same treatment that someone has given you, whether it's good or bad.
If you give someone a gift for his birthday, he'll likely give you one once your birthday rolls around. If you give him nothing, it's probably best not to expect anything in return.
Very rarely do people give without first getting something themselves. More often that not, acts of kindness are rooted in those that came prior. It's a "you do, I do" dynamic. It's almost like playing tag.
The same goes for negative behavior. If someone does something to upset you, your first instinct is to do the same to them.
In reality, though, the best relationships are those where you do someone nice for someone else and expect nothing in return. They'll felt a sense of duty to return the favor, though, because we don't want to create the perception that we're unappreciative or taking advantage of the other person's goodwill. In addition, giving just tends to make us feel better than receiving.
We should always aim to do good things for people even when they haven't done anything for us. Did your close friend not give you anything for your birthday this year? Maybe she had a legitimate reason for not doing so, like being strapped for cash. When her birthday comes around, give her something -- anything -- even if it's a small trinket. I guarantee she'll appreciate the gesture, which will only serve to deepen your bond.
Of course, if you've given your friend birthday gifts for, say, seven consecutive years and have gotten none from her over that span, there comes a point where you start to wonder whether the person is flat-out frugal or indifferent.
Have you noticed this principle of reciprocity at work in your life?