How do I know where to place adjectives in French

In French, adjectives are usually placed after the noun they are describing (la voiture blanche = the white car) unlike in English where the adjective is placed before the noun. However, as always, French has a few exceptions to this rule. These exceptions can be remembered using the acronym "BAGS". B stands for beauty. Thus any adjective relating to beauty (Beau / Joli) are placed before the noun, just like in English. A stands for age (Vieux / Jeune), G stands for Good or Bad (Bon / Mauvais) and S stands for size (Petit / Haut / Gros). Thus, the white car is "la voiture blanche", but the big car is "la grande voiture."

Other exceptions are adjectives with more than one meaining, such as "ancien". "Un ancien prof" means a former teacher because the adjective ancien is before the noun. But, "Une maison ancienne" means an old house because the word ancienne is after the noun.