How can one know that God is pleased with him so that he may be assured that his acts of worship are sufficient to enter Paradise?

A servant cannot definitively know whether God is pleased with him or displeased. However, he must act upon what God has enjoined and abandon what He has forbidden, while contemplating God's pleasure. God has promised the believing, righteous, and pious ones, who perform good deeds, success in attaining Paradise and salvation from Hellfire, and He does not break His promise. It is not just that a believer performs acts of obedience and then they are not accepted, unless he associates partners with God or acts hypocritically. A Muslim should have a good opinion of his Lord, fear a bad ending, hope for his Lord's mercy, fear His punishment, and not despair of His mercy.