How to tell the difference between latin noun cases?

I'm studying for my latin final, and Im having trouble with translating nouns in certain cases. how can you tell if a noun ending in '-is' is 1st/2nd declension plural dative, 1st/2nd declension plural accusative, or 3rd declension singular genitive? or how do you tell if '-ae' or '-i' is singular genitive or plural nominative? There are so many overlapping endings I get really confused. Sometimes I can use the context of the sentence to figure it out, but that can be really tricky. Is there an easier way to tell? Or does someone have a tip for using context clues to tell?