i use these two acronyms LONERS and DionZA any noun ending with the letters L, O, N, E, R, S are usually masculine. any noun ending with the letters D, -ion , Z, A are usually feminine. There are exceptions and those you will have to learn case by case like el agua. Hope this helps

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Learning the genders of the nouns is you memorizing them so las llaves, los paquetes, las flores. For the most part if it ends in an O then it's el or los (os-plural) and if it ends in A then it's la or las (as-plural).