Know your value
And if people don't know or appreciate your value, get out of dodge. Immediately.
I would venture to say that we've all felt ignored, under appreciated, taken advantage of or just plain poorly treated at some point in life. People have bad days, it happens - but if it becomes a trend, you must re-evaluate your role and make the necessary changes.
For example, if you are good friend to somebody, they should be a good friend to you. If that's not the case, the relationship is not mutually beneficial and therefore serves no purpose in your life. Why be trustworthy, loyal and kind to somebody who doesn't do the same in return?
And in this economy, I know we are all lucky to have jobs, but if your hard work goes completely unnoticed and unappreciated, you are probably not in the right position. While circumstance differ for everyone, I suggest getting out of this type of situation as soon as possible. Because eventually it will affect your work ethic and view of authority - or make you an incredibly bitter person who's no fun to be around. And no one wants that, right?
Perhaps one of the most important times to recognize your value, is within a relationship. I too often see people stuck in unhappy relationships, or even marriages, who stay because of fear, familiarity or they just plain and simple don't know their value.
You should never settle. You are never going to amount to anything, if you don't realize that you have something great to offer the world. If you surround yourself with people who treat you poorly and bring you down, you are on your way to living a perpetually sad and miserable life. And it will be no one's fault but your own.
It is your responsibility to know your value in life, and go after what you want. If you are not happy about a certain aspect, or with certain people in your environment - change it. Don't be afraid of change. It's healthy.