1. Read the parable within its context. Know what was happening before Jesus started to say it.
2. Note what, if anything, Jesus said after the parable.
3. Know who the parable was addressed to - the disciples, the people in general, a particular person. This knowledge will help you to understand it properly.
4. Note the points of references. For example in Luke 7:36-50, the point of reference are the moneylender (or creditor) and the two debtors. In this story, someone in the audience, Simon, would have been judged by the story while the harlot would have witnessed mercy. Judgement and mercy become lessons that this parable teaches.
5. The lessons and morals from a parable are supposed to be obvious. Do not attempt to ?add things? that are not in the story.
In Luke 8:9-10 and Mark 4:10-12 Jesus quotes from Isaiah 6:9-10 when he says ?though seeing, they may not see; though hearing, they may not understand'. This has led some people to assume that we cannot understand the parables of Jesus. This is not the case as you can observe in Mark 12:12. If you go back to Mark 11 you will get the context into which Jesus was speaking. He was addressing the chief priests, the teachers of the law. Mark 12:12 makes it clear they understood him.
People with hardened hearts will not appreciate the parables. They will always apply the teachings to someone else and not themselves. You do not have to have a hardened heart. You can understand the parables of Jesus. Even a non-Christian with an open heart can understand them.