Do you know anyone who lives this way consistently? Our culture and media in the west seems to condition us toward putting oneself first. How would you suggest one can overcome selfishness?
Why are you introducing the requirement that they should do this consistently? I've seen reports of many instances of ordinary people who have made a difference in their community in various ways, putting others before themselves. All the time? Probably not, but so what?
Frankly, it is irrelevant whether one person has done this, or one million, or one billion. My initial remark was a question: would we not consider someone who acted selflessly for others, without any expectation of a reward in an afterlife, be a "better" person than a practising Christian?
Rather than answer that question ToBeLoved has preferred to argue (ineffectively) that, firstly, Christians are definitely better, and secondly, the type of person I have posited does not (indeed cannot) exist.
You ask how would I suggest one can overcome selfishness.
1. I'm not clear in what way that question is relevant to your OP.
2. I'm not clear in what way that question is relevant to anything I have posted.
3. I'm not clear why you think I might have some insight into combating selfishness.
That said, here are my cursory thoughts on the matter. Rather than think in terms of selfishness we would be better to think in terms of responsibility. A very young child is responsible only for themselves. They must learn, with parental guidance, not to put their hand in a fire, or to run out into traffic. Since their responsibility is inward looking they may be perceived as selfish.
Then the parents extend the responsibility, "Let Jane play with your toys for a while", making the child partially responsible for the happiness of their sibling. When we accept responsibility for others, and act upon that acceptance, selfishness is automatically subdued or eliminated.
So, my solution is to accept responsibility. The more responsibility we accept the more difficult it becomes to be selfish. Of course, you may then reasonably ask, how do we get people to accept responsibility? That would be a political question and this is Ethics and Morality.