You do this by the faith that you profess and the godly life that flows from it. In the past as I have dealt with certain biblical figures in preaching I have been left to construct an argument that would favor their entrance into heaven (think of men like Samson and Solomon). I have often urged people to live in such a way that the one conducting your funeral does not have to labor to convince themselves that there is reason to be hopeful. Not surprisingly, J. C. Ryle said it before I did and much, much better than I could. So, here are his words from the book, Holiness.
When we have carried you to your narrow bed, let us not have to hunt up stray words, and scraps of religion, in order to make out that you were a true believer. Let us not have to say in a hesitating way one to another, “I trust he is happy; he talked so nicely one day; and he seemed so please with a chapter in the Bible on anther occasion; and he liked such a person, who is a good man.” Let us be able to speak decidedly as to your condition. Let us have some solid proof of your repentance, your faith, and your holiness, so that none shall be able for a moment to question your state.
Depend on it, without this, those you leave behind can feel no solid comfort about your soul. We may use the form of religion at your burial, and express charitable hopes. We may meet you at the churchyard gate, and say, “Blessed are the dead that die in the Lord.” But this will not alter your condition! If you die without conversion to God, without repentance, and without faith–your funeral will only be the funeral of a lost soul; you had better never have been born.”