It is true that one can only be saved by faith in the Lord Jesus Christ (Eph. 2:8-9), and the reason is so that no one can boast before God. However, what constitutes Christian good works? The apostle James tells us in James 2:14-17, "What good is it, my brothers, if a man claims to have faith but has no deeds (good works)? Can such faith save him? 15 Suppose a brother or sister is without clothes and daily food. 16 If one of you says to him, "Go, I wish you well; keep warm and well fed," but does nothing about his physical needs, what good is it? 17 In the same way, faith by itself, if it is not accompanied by action, is dead" (NIV).
Here James clearly pointed out that good works is doing what Jesus said to do, loving ones neighbour. So good works cannot save a person, but the fruit of true saving faith is works that show love to others, rather than hatred, selfishness and murder.
John the Baptist taught this also in Luke 3:7-14, "John said to the crowds coming out to be baptized by him, "You brood of vipers! Who warned you to flee from the coming wrath? 8 Produce fruit (good works) in keeping with repentance. And do not begin to say to yourselves, `We have Abraham as our father.' For I tell you that out of these stones God can raise up children for Abraham. 9 The ax is already at the root of the trees, and every tree that does not produce good fruit will be cut down and thrown into the fire." 10 "What should we do then?" the crowd asked. 11 John answered, "The man with two tunics should share with him who has none, and the one who has food should do the same." 12 Tax collectors also came to be baptized. "Teacher," they asked, "what should we do?" 13 "Don't collect any more than you are required to," he told them. 14 Then some soldiers asked him, "And what should we do?" He replied, "Don't extort money and don't accuse people falsely--be content with your pay" (NIV).
So here we can see that good works can be done directly by way of helping others and indirectly by way of not sinning against others.
Finally, Jesus explained in Jn. 6:28-29, the ultimate good work that all people need to do, "Then they asked Him, "What must we do to do the works God requires?" 29 Jesus answered, "The work of God is this: to believe in the One He has sent (Himself)" (NIV). So here we can see that the first good work that anyone can do is believe in the Lord Jesus Christ. That He is God's eternal Son, sent into this world to die on the cross for sinners.
Therefore, good works is loving God and loving ones neighbours.