To be sure whether you are going to heaven takes the grace of God. It is not easy to be sure if we are going to heaven because of numerous sins we have on our record which must be forgiven by God to confirm yourself eligible for the kingdom of heaven. As a Christian, serving the God in the right way and sticking to his way by praying, studying the Bible and so on makes us eligible for heaven. It's conscience, for instance, a sinner knows that what he or she is doing at a particular time is wrong and highly disregarded by God. So if you are doing things contrary to the ways of God, you know automatically that you are not ready for heaven and so you need to repent and ask God for forgiveness of sins. But if you are doing things that are of God and you feel you are on the right track with the lord, you would be definitely sure of making heaven.
By glorifying God's name, obeying and keeping his commandments, you are definitely on your way to the kingdom of heaven but if you do otherwise you are not on heaven way.