It's very difficult to give you rules for 'noun phrase', which just means a word or groups of words including a noun. The ude of the term phrase for a single word is used by linguists so that they can divide a sentence into NP and VP, etc. All the words associated with a noun make up the noun phrase, which could incluse articles, adjectives, prepositions, adverbs (modifying adjectives) and other noun working as adjectives. The are rules about individual things like how to make compound nouns plural. If you ask more specific questions or give us examples of phrases you want looking at, then you'd probably get more concrete answers.