The first thing we should do with a parable is not to go beyond what was originally intended to be said, but to stay within the confines of the message. As we read the parable don't make it say more than it was intended to.

A look at 'The parable of the sower' in Luke 8: 4-8 is a good one to study for the simple reason that Jesus himself ( Luke 8: 11-15) then goes on to give us the interpretation!

The story has two principal parts, the seed and the types of soil into which the seed is sown. The parable deals with the different situations that arise when the Word of God is sown into lives. Incidentally, although it is called The parable of the sower, it is not actually about the sower!

To establish rules in interpreting parables, let us look at another well-known one, 'The parable of the Good Samaritan.' (Luke 10: 29-37)

Always try to determine the purpose of the parable.
What was the reason why Jesus told the story? The answer is right at the beginning as the parable was told in response to someone who wanted to justify himself. Every parable will have one major purpose.

Don't build doctrines on the minor details of the story.
The Samaritan took out two silver coins. Is there any significance in that? And if there is and it is minor, then don't allow that to become the main thrust of the story. Don't draw something out if it is not there.