It depends on ones definition of a 'saint'.
Saints in Hinduism and Buddhism (in its various asian forms) are great spiritual teachers. They are usually acclaimed saints.
In Christianity, Saints are persons who have furthered the teachings of the Church (i.e. Saints proclaimed Doctor of the Church), or people who have lived exceptionally holy lives to be a role model for other spiritual aspirants. Sainthood requires at least two medically verifiable miracles. Martyrdom requires that you not recant the faith.
So in summary, we might say, in general to become a saint in the Christian sense you first have to die having lived a life which is not morally questionable or against the teachings of the Church.
Performing 'miracles' or notable charitable deeds helps, as does defending Christian principles against adversity or persecution.
After death, the relevant Church has to confirm that your life is spiritually and morally unquestionable, and in some cases that there have been apparent miracles granted to those visting your tomb. The formal processes by which a 'deceased' individual becomes a saint are Beatification and Canonisation.
A word of caution though, it can take a long time after death to become a saint in the formal sense.