?Masculine (der):

Male persons and animals
days of the week, months of the year
seasons, and most weather elements
car makes
monetary units
non-German river names
rocks and minerals
mountains and mountain ranges
and alcoholic and plant-based drinks

?Feminine (die):

Female persons and animals
Rivers within Germany, Austria, Switzerland
Airplanes, motorcycles, ships
Numbers used as nouns
Trees, fruits, and flowers
Nouns formed from measurement or size adjectives

?Neuter (das):

Young persons and baby animals
metals and chemical elements
names of continents, cities, provinces, and most countries
scientific units & measurements
letters of the alphabet and music notes
hotels, cafes, restaurants, and movie theaters
other parts of speech used as nouns (gerunds, colors, languages, English -ing forms).