The articles
Singular nouns take de when they are masculine or feminine and het when they are neuter, and every plural takes de. The indefinite article een (a, an) goes with every singular noun, but plurals have none: een boek, boeken.
What the noun means
Sometimes what a noun means tells you its article.
Nouns for people take de. Exceptions: het kind, het lid, het slachtoffer, and het meisje (a diminutive, so het).
Exceptions
childBreaks the people rule: a child is a person, yet it is het kind. memberBreaks the people rule: a member is a person, yet it is het lid. victimBreaks the people rule: a victim is a person, yet it is het slachtoffer.
Currencies take de: de euro, de dollar. Exception: het pond.
Examples
peseta (old Spanish money)
Exceptions
poundBreaks the currency rule: currencies are de, but it is het pond.
Most sports take het: het tennis, het hockey.
Examples
football (the sport)As the sport it is het voetbal; the ball itself is de voetbal. volleyball (the sport)As the sport it is het volleybal; the ball itself is de volleybal.
Languages take het: het Nederlands, het Engels.
Examples
Chinese (language)As the language it is het Chinees; a Chinese man is de Chinees.
Most materials take het: het hout, het goud. Exceptions: de wol and de zijde.
Examples
cotton (fabric)As the fabric it is het katoen; the cotton plant is de katoen.
Exceptions
woolBreaks the materials rule: most materials are het, but it is de wol. silkBreaks the materials rule: most materials are het, but it is de zijde.
When the infinitive of a verb is used as a noun, it always takes het: eten → het eten.
Endings
The ending of a noun often tells you its article.
Nouns ending in -ing take de. Many are made from a verb: verzamelen → de verzameling.
Adding -in to a noun makes its female form, which takes de: vriend → de vriendin, koning → de koningin.
Examples
female friend, girlfriend
Nouns ending in -heid take de. Many are made from an adjective: vrij → de vrijheid.
Nouns ending in -nis take de: de kennis, de gebeurtenis.
Nouns ending in -te take de: de warmte, de hoogte. This works even when -te is not a real suffix, as in de lente.
Nouns ending in -de take de. Many are made from an adjective: lief → de liefde.
Nouns ending in -teit take de: de kwaliteit, de universiteit.
Nouns ending in -ij take de: de bakkerij, de boerderij.
Nouns ending in -ie take de: de politie, de televisie. This works even when -ie is not a real suffix, as in de koffie.
Nouns ending in -isme take het: het toerisme, het realisme. Many are like English words ending in -ism.
Nouns ending in -asme take het: het enthousiasme, het sarcasme.
Nouns ending in -ment take het: het moment, het argument.
Nouns ending in -sel take het. Many are made from a verb: voeden → het voedsel.
Examples
lidThe usual form is het deksel, but you may also hear de deksel.
A diminutive (a small form ending in -je or -tje) always takes het, even when the base word takes de: de tafel → het tafeltje.
Examples
girlA diminutive of meid (girl); every diminutive is het.