Ok, before I start here I want to say that this is only a generalization compiled from previous prophecies and omens in the series. Many times, the full meaning of a prophecy can not be understood until it is fulfilled. With that being said, here are some tips and hints on how to interpret prophecies, omens, and other signs that occur in the warriors series.
1. Beware of Multiple Meanings
Many times, prophecies can have more than one meaning. For example Bluestar's Prophecy - Firestar's Quest Spoiler. When a prophecy is fulfilled, don't completely forget about it, (especially if it is a major prophecy) because it may come up again later.
2. Pay Attention to Future Events
When you first come across a prophecy or omen, it is almost impossible to determine the meaning. Future events will almost certainly have a major effect on your interpretation of a prophecy or omen. Always remember previous prophecies as you continue reading, and don't forget them until they are fulfilled. Sometimes, you might be able to use previous prophecies in conjunction with other clues to discover astonishing secrets. For more information on this, see my article on How to guess what's happening before anyone else.
3. Pay Attention to the Characters
Pay attention to what the characters think about a particular prophecy or omen. (Especially Medicine Cats) Their interpretations are not always right, but they can help get you thinking along the right lines, and may explore possibilities that you may not have considered. When considering this however, remember to expect the unexpected. (See Below) Characters are not always right, and they can mislead you if you are not careful.
4. Expect the Unexpected
This almost goes without saying. Prophecies and omens to not always mean what they seem to mean. Many times you may think that you have determined the meaning of a prophecy, but it will turn out to be referring to something different entirely. Many prophecies use figurative language, and sometimes it is difficult to determine whether a prophecy or a particular part of a prophecy is literal or figurative. Usually when a prophecy does not have a clear literal meaning, it can be interpreted as being figurative.