Selfish individuals have existed as long as anyone can remember. They have destroyed friendships, caused wars and broken hearts. Selfishness itself is defined as caring and promoting ones self to the exclusion of others. Being selfish is something people tend to look down upon.
Unfortunately, selfishness is a core part of human nature. Everyone is selfish at one point or another in their life. Many have argued that altruism is the lack of selfishness. The most selfless act has benefits for the one doing it. People are simply deluding themselves when they believe they are being altruistic.
It is very difficult to change ones nature. If people are naturally selfish, maybe we should find a way to work this into how we live. Having selfish behavior is not necessarily bad. Self-preservation is a good example of this. However, self-preservation at the expense of others is not so good.
One way to act selfish and still be a reasonable human being is to consider who your selfishness effects. Step back and consider how your actions affect others over time. When looking at the world from this view point, it is entirely possible to be extremely selfish and still leave others unaffected by your actions. You may even be able to help them. Strictly speaking, this is not the definition of selfish, as you aren't hurting others to help yourself.
One can do this by looking at the long term effect of their actions. Doing things that help others will nearly always help you later on. Helping someone in pain, at cost to yourself, may make you feel better about yourself. Sometimes, causing someone pain now will be better for them (and you) in the long term. If more people thought more selfishly given the parameter of time, then the world would be a better place. People should stop lying to themselves and work with who they are.